The different telescopes of the network are getting online for the season. we start with the peak of the very high magnification event OGLE 2007-BLG-050/MOA 2007-BLG 103.
As announced in PLANET Anomaly Update 2006 #14-2 (issued 18-Aug, 6:15 UT), PLANET data collected with the SAAO 1.0m (Sutherland, South Africa) and the Danish 1.54m at ESO LaSilla (Chile) show a flat and later slowly falling light curve for OGLE 2006-BLG-450 after HJD=2453965.231 (17-Aug, 17:33 UT), favouring a previous caustic exit to have occured.
Already with the first release of data by OGLE on 12-Aug, the event OGLE 2006-BLG-450 was considered to be due to a binary lens, where a caustic entry had already taken place, but was not covered densely enough in order to clearly reveal the nature of the event. Since extended caustics, which are characteristic for lens binaries or multiples (including stars orbiting planets), form closed curves, caustic passages occur in pairs of entries and exits, provided the size of the caustics exceeds the angular size of the observed source star. Therefore, a further observed rise should indicate a caustic exit to occur. But OGLE 2006-BLG-450 reached a maximum that did not correspond to caustic exit near HJD=2453962.7 (15-Aug, 5:00 UT) and was considered falling before a strong rise was first reported by OGLE, whereas PLANET Anomaly Alert 2006 #14 (issued 17-Aug, 7:00 UT) stated that earlier PLANET data collected with the SAAO 1.0m (Sutherland, South Africa) after HJD=2453964.337 (16-Aug, 20:05 UT) showed a brightening by 0.1 mag, indicating a smooth rise after HJD=2453963.7 (16-Aug, 5:00 UT). Further data collected with the Danish 1.54m at ESO LaSilla (Chile) revealed a continuation of this rise with increasing slope, which tended to become constant in the most recent data until HJD=2453964.724 (17-Aug, 5:22 UT). While this could have been the anticipated caustic exit, models without caustic passages looked possible. Further PLANET data, now collected with the Canopus 1.0m (near Hobart, Tasmania) showed OGLE 2006-BLG-450 falling between HJD=2453964.853 (17-Aug, 8:28 UT) and HJD=2453964.987 (17-Aug, 11:41 UT), as reported in PLANET Anomaly Update 2006 #14-1 (issued 17-Aug, 14:05 UT), but the characteristic slope discontinuity marking the end of a caustic exit had not been observed (yet?).
In PLANET Anomaly Alert 2006 #13 (issued 15-Aug, 7:30 UT), we reportet that data collected on MOA 2006-BLG-132 by PLANET with the Canopus 1.0m (near Hobart, Tasmania) after HJD=2453962.010 (14-Aug, 12:14 UT) showed a stronger rise than predicted by a previous model and refused to be explained by microlensing of a point source due to a single star. This stronger rise appears to coincide with the second half of a dip observed by MOA after HJD=2453961.796 (14-Aug, 7:06 UT).
Following secondary alerts by MOA and OGLE in OGLE 2006-BLG-435 = MOA 2006-BLG-126, PLANET collected data with the Canopus 1.0m (near Hobart, Tasmania) after HJD=2453951.95 (4-Aug, 10:48 UT), showing that the caustic was exited very quickly before HJD=2453951.903 (4-Aug, 9:41 UT). The source radius crossing time was less than 15 min, as reported in PLANET Anomaly Alert 2006 #12 (issued 4-Aug, 15:15 UT).
OGLE 2006-BLG-277 caustic exit was finally observed at HJD=2453951.11 (August 3, 14:43 UT), from OGLE and Canopus 1.0m (near Hobart, Tasmania), as described in PLANET Anomaly Update 2006 #9-3 (issued 3-Aug, 14:30 UT).
In PLANET Anomaly Update 2006 #11-1 (issued 22-Jul, 14:50 UT) we reported that data collected by PLANET using the Danish 1.54m at ESO LaSilla (Chile), and the Canopus 1.0m telescope (near Hobart, Tasmania), as well as OGLE data, show that OGLE 2006-BLG-375 is rising towards a caustic exit at approximately 2453939.26 (July 22.76 UT).
After the OGLE team reported that the brightness of OGLE 2006-BLG-375 increased by about 1 mag as compared to the previous night, we reported in PLANET Anomaly Alert 2006 #11 (issued 21-Jul, 11:20 UT) that data collected by PLANET with the Canopus 1.0m (near Hobart, Tasmania) show a nearly flat light curve until HJD=2453937.189 (20-Jul, 16:32 UT), while data from the Danish 1.54m at ESO LaSilla (Chile) after HJD=2453937.645 (21-Jul, 3:29 UT) and more recent data from the Canopus 1.0m reveal that the source star has entered a caustic and the event was flattening to a plateau region between fold-caustic passages.
After OGLE had pointed to a rise by 0.35 mag on OGLE 2006-BLG-398 during one night that was not matched by an ordinary light curve, PLANET collected data with the Canopus 1.0m (near Hobart, Tasmania) after HJD=2453934.913 (18-Jul, 9:55 UT). In PLANET Anomaly Alert 2006 #10 (issued 18-Jul, 13:45 UT), we reported that the the first three points show a rise by 0.35 mag during 1.6 hrs at increasing slope, while the fourth point is about 0.9 mag below the preceding one. Together with the previous OGLE data, the observations appear to follow the characteristic rise to a caustic exit for a small, strongly blended source. Since for faint stars, microlensing essentially works as a caustic-crossing detector, such light curves are not unusual.
As pointed out in In PLANET Anomaly Update 2006 #9-2 (issued 17-Jul, 5:35 UT), further data collected on OGLE 2006-BLG-277 with the Perth 0.6m (Bickley, Western Australia) and the Danish 1.54m at ESO LaSilla (Chile) reveal flattening towards a plateau region and show that the source entered the caustic already at HJD=2453932.78 +/- 0.01 (16-Jul, 6:45 UT +/- 15 min), after which a brightening by about 1.7 mag until the reported caustic peak was reached. The strong brightening strongly disfavours a planetary origin.
As reported in PLANET Anomaly Alert 2006 #9 (issued 16-Jul, 15:15 UT), a sequence of five data points collected by PLANET on OGLE 2006-BLG-277 with the Canopus 1.0m (near Hobart, Tasmania) after HJD=2453932.889 (16-Jul, 9:20 UT) show a rise by ~ 0.6 mag that follows the characteristic shape of a fold-caustic entry. The presence of extended caustics is a unique signature of companions to the lens star. In PLANET Anomaly Update 2006 #9-1 (issued 16-Jul, 19:25 UT), we reported that further PLANET data collected with the Canopus 1.0m (near Hobart, Tasmania) and the Perth 0.6m (Bickley, Western Australia) reveal a caustic peak at HJD=2453933.17 +/- 0.01 (16-Jul, 16:05 +/ 15 min). Since no change of the sign of curvature indicating an approach to a plateau region between fold-caustic passages had been observed by then, it was considered more likely that the source has touched a cusp resulting in a single caustic peak.
As reported in PLANET Anomaly Alert 2006 #8 (issued 9-Jul, 7:00 UT), PLANET data collected on OGLE 2006-BLG-359 during the most recent night with the Danish 1.54m telescope at ESO LaSilla (Chile) indicate that this event is approximately 2.5 mag brighter than it was 2.5 days ago and over the last few hours has risen at the rate of approximately 1.5 mag per day. We consider either a caustic crossing is currently in progress or the lensed star being heavily blended at a magnification A ~ 60 now and approaching A0~465 at peak, predicted for HJD = 2453926.5 (10-Jul, 0:00 UT).
In PLANET Anomaly Alert 2006 #7 (issued 6-Jul, 8:40 UT), we report an brightening of ~ 0.5 mag on OGLE 2006-BLG-355 within the previous 24 hours in deviation from a point-source point-mass lens light curve seen in data collected with the Danish 1.54m at ESO LaSilla (Chile). Subsequently, in PLANET Anomaly Update 2006 #7-1 (issued 6-Jul, 10:30 UT) we reported a more prominent brightening by 2 mag indicated by data collected at the Danish 1.54m at ESO LaSilla (Chile), followed by a sudden drop by about 1.5 mag within 15 minutes indicated by data collected with the Canopus 1.0m (near Hobart, Tasmania). However, the latter turned out to be a relict of the effect of a nearby star on the data reduction.
After an excellent coverage of the caustic entry of OGLE 2006-BLG-335 after its peak and the plateau region with data from the Danish 1.54m at ESO LaSilla (Chile), the Canopus 1.0m (near Hobart, Tasmania), and the Boyden 1.5m (Bloemfontein, South Africa), we observed a rise, reported in PLANET Anomaly Update 2006 #6-3 (issued 5-Jul, 7:50 UT), the expected fold-caustic exit peak, reported in PLANET Anomaly Update 2006 #6-4 (issued 5-Jul, 14:45 UT), and finally the end of the caustic exit, where the trailing limb of the caustic has been found to have exited at HJD=2453922.159 +/- 0.001 (5-Jul, 15:49 UT +/- 1 min), observed with the Canopus 1.0m (near Hobart, Tasmania), as reported in PLANET Anomaly Update 2006 #6-5 (issued 5-Jul, 17:10 UT). The large magnification in the plateau region also favours a stellar binary lens over a planetary explanation. However, with a coverage of two caustic passages, the nature of the event should be well-constrained and a reliable measurement of the stellar brightness profile is expected.
In PLANET Anomaly Update 2006 #6-1 (issued 1-Jul, 23:20 UT) and PLANET Anomaly Update 2006 #6-2 (issued 2-Jul, 2:25 UT), we reported rapid brightening on OGLE 2006-BLG-335, mentioned earlier by OGLE. PLANET data collected with the Canopus 1.0m (near Hobart, Tasmania) allows to determine the beginning of the caustic entry to have occured at HJD=2453918.22 +/- 0.02 (1-Jul, 17:20 UT +/- 50 min).
As reported in PLANET Anomaly Alert 2006 #6 (issued 29-Jun, 12:45 UT), PLANET data collected on OGLE 2006-BLG-335 with the Canopus 1.0m (near Hobart, Tasmania) and the Danish 1.54m at ESO LaSilla (Chile) after HJD=2453914.98 (28-Jun, 11:30 UT) seem to deviate from a model light curve through the previous points assuming a single lens and a point-like source star. Similar behaviour in the OGLE data had previously been reported by the OGLE team. Trying to revise the model to account for all data leaves us with a small deviation for earlier epochs as well as unreasonable blend ratios. While OGLE 2006-BLG-335 poses a challenge for obtaining a reliable light curve, it does not appear unlikely that we observe a short 10-15% deviation lasting about 1.5 days, which now approaches its end. Most recent data from the Canopus 1.0m, from HJD=2453915.95 (29-Jun, 10:45 UT) onwards, confirm this trend. The significance for the anomaly will increase with further data being collected, which will better constrain the (background) single-lens model and in particular the blend ratio.
After the OGLE team pointed to ongoing microlensing of a source that shows periodic variability in OGLE 2006-BLG-357, PLANET/RoboNet added this event to its monitoring programme. A model by Lukasz Wyrzykowski (on behalf of the OGLE team) based on a Fourier analysis of the variable baseline yields a period of about 0.75 days, so that rapid variations of the observed magnitude can be expected while the source undergoes microlensing. According to that model, the expected peak magnification is A0 ~ 1.8, reached at HJD = 2453913.489 (26-Jun, 23:45 UT). More information is available on Lukasz' Variable Events Warning system (VEWS) pages.
In PLANET Anomaly Alert 2006 #5 (issued 17-Jun, 8:35 UT), we reported that PLANET data collected on OGLE 2006-BLG-304 (identical to OGLE 2006-BLG-307) with the SAAO 1.0m (Sutherland, South Africa) during the recent night showed a rise consistent with the approach to a fold-caustic, while subsequent data collected at the Danish 1.54m at ESO LaSilla (Chile) confirmed this by initially showing an even steeper rise. This rise, up to the caustic exit peak, has also been reported by the OGLE team. Further Danish 1.54m data cover the caustic exit peak and revealed the event falling fast with a caustic exit to be expected very soon. In fact, as reported in PLANET Anomaly Update 2006 #5-1 (issued 17-Jun, 9:15 UT), data from the Danish 1.54m at ESO LaSilla (Chile) revealed that the source star completed the caustic exit at JD=2453903.8629 +/- 0.003 (17-Jun, 8:42:35 UT +/- 25 sec).
In PLANET Anomaly Alert 2006 #4 (issued 7-Jun, 22:00 UT) and PLANET Anomaly Update 2006 #4-1, we reported that PLANET data collected with the SAAO 1.0m at Sutherland (South Africa), the Canopus 1 m telescope at Hobart, Tasmania (Australia) and the Danish 1.54m at ESO LaSilla (Chile) reveal that the source star in event MOA 2006-BLG-003 underwent a caustic crossing. The apparent caustic entry started at HJD=2453861.85, whereafter the source became 1.5 mag brighter over the next approx. 12 hours. In PLANET Anomaly Update 2006 #4-3 , we reported that the caustic exit took 0.435 days with the trailing limb exiting the caustic at JD=2453900.87.
We reported in PLANET Anomaly Alert 2006 #3 (issued 22-May, 18:55 UT) that data collected during the recent night by PLANET with the Danish 1.54m telescope at ESO LaSilla (Chile) as well as OGLE data reveal an anomalous behaviour of event OGLE 2006-BLG-238. The event appeared 0.4 mag brighter than predicted for that epoch. A round top is indicated, compatible with a deviation lasting about half a day. In order to determine the nature of the event, further dense monitoring is required and encouraged. The source star might have hit a caustic created by a stellar lens binary, but this kind of deviation also does not seem unlikely to have been caused by a planet orbiting the (single) lens star.
In PLANET Anomaly Update 2006 #2-1 (issued 7-May, 6:55 UT), we reported that PLANET data collected with the Danish 1.54m telescope at ESO LaSilla (Chile) and the Perth 0.6m telescope (Western Australia) reveal that the source star in event OGLE 2006-BLG-207 transited a caustic structure within just 1 to 1.5 days, where two peaks separated by a local minimum at around 2.45 mag above baseline occured.
In PLANET Anomaly Alert 2006 #2 (issued 6-May, 7:25 UT), we reported that recent PLANET observations on OGLE 2006-BLG-207 with the Danish 1.54m telescope at ESO LaSilla taken between HJD=2453861.691 (6-May, 4:34 UT) and HJD=2453861.784 (6-May, 6:50 UT) show a sudden rise by about 1 mag that does not match a smooth slope of the light curve, so that a caustic entry is indicated. In order to determine the nature of this event, further observations are required. The newest developments can be seen in our light curve.
As announced in PLANET Anomaly Alert 2006 #1 (issued 30-Apr, 9:00 UT), PLANET will start into the 2006 observing season today (1-May). We aim to concentrate on providing high-quality photometry with a new data reduction pipeline based on image subtraction. According to an agreement between PLANET and RoboNet, all data collected will form part of the PLANET/RoboNet campaign and is considered to be common intellectual property.
As reported in the 26-Jan-2006 issue of Nature, the PLANET/RoboNet campaign, together with OGLE and MOA, found evidence for a cool rocky/icy planet in event OGLE 2005-BLG-390 with only 5 Earth masses (uncertain within a factor of two) around a red dwarf. The light curve initially followed the characteristic brightening expected for a single isolated lens star and a point-like source star, which in this case is a G2-4 giant, and reached a peak magnification of about 3 on 31-Jul. However, on 10-Aug, an anomalous rise by 0.15 mag was observed by PLANET/RoboNet with the Danish 1.54m at ESO LaSilla (Chile), while an OGLE point from this night showed the same trend. By succeeding in monitoring the second half of this anomaly, lasting about half a day, with the Perth 0.6m (West Australia), and previously obtaining a dense coverage of the peak region of the event, we were able to conclude that the lens star is orbited by a low-mass planet, which is designated OGLE 2005-BLG-390Lb. The MOA collaboration was able to identify the source star on its frames and confirmed the observed deviation. More information can be found in a related ESO press release as well as in our detailed description. We have also provided tailored information for journalists including tailored press releases in several languages targetting different geographical regions. A full-text version of the discovery paper (2006, Nature 439, 437-440) as well as a preprint (astro-ph/0601563) can also be accessed.
As announced in PLANET anomaly 2005 #12 (issued 16-Aug, 14:30 UT), PLANET data of OGLE 2005-BLG-434 taken with the Danish 1.54m at ESO LaSilla (Chile) and the SAAO 1.0m at Sutherland (South Africa) reveal a short duration anomaly near peak at August 13, 2005. The nature of the anomaly is not known yet, potentially of extreme binary or planetary nature. Further observations are encouraged in order to better constrain the anomaly.
The observation of another caustic entry in OGLE 2005-BLG-327 was reported in PLANET anomaly update 2005 #10-6 (issued 15-Aug, 7:40 UT) after the event rose slightly during the preceding two weeks. PLANET data taken with the Danish 1.54m at ESO LaSilla (Chile) indicate an increase by about 2.8 mag from HJD=2453596.6225 (14-Aug, 2:56 UT) and HJD=2453597.7503 (15-Aug, 6:00 UT), where the source has likely entered a caustic between the former epoch and HJD=2453596.7259 (14-Aug, 5:25 UT). Continued dense monitoring will provide powerful constraints on the nature of the lens system, including the potential assessment of annual parallax effects and the orbital lens motion. Moreover, caustic passages under different angles enhance the opportunities for measuring the brightness profile of the source star.
As announced in PLANET anomaly 2005 #11 (issued 11-Aug, 13:45 UT), PLANET data of OGLE 2005-BLG-436 taken with the Danish 1.54m at ESO LaSilla (Chile) and the SAAO 1.0m at Sutherland (South Africa) reveal a deviation of the lightcurve from the PSPL model near maximum. This is presumbaly an effect of the finite source star. The baseline brightness of the source star is I = 16.05 (determined by the OGLE team), it is currently magnified by about a factor of 7.5 (2.2 mag).
As announced in PLANET anomaly update 2005 #10-5 (issued 30-Jul, 8:35 UT), PLANET data taken with the Danish 1.54m at ESO LaSilla (Chile) during the night starting 29-Jul indicate a decrease of OGLE 2005-BLG-327 by less than 0.2 mag/day. Our observations show that the source is expected to have left the caustic between HJD=2453580.815 (29-Jul, 7:33 UT) and HJD=2453580.820 (29-Jul, 7:41 UT) after it took between 20 and 21.5 hrs to cross it.
In PLANET anomaly update 2005 #10-4 (issued 29-Jul, 8:15 UT), we reported that we succeeded in observing OGLE 2005-BLG-327 during most of the second half of the caustic exit of OGLE 2005-BLG-327 with the Danish 1.54m at ESO LaSilla (Chile), where a typical sampling interval of 3 min provides a quasi-continuous coverage. Moreover, prior to these data, about 40 points have been taken with the SAAO 1.0m at Sutherland (South Africa). Independently, the OGLE team reported that their data show a fading by more than 2 mag during the recent night. With the last Danish 1.54m data point taken at HJD=2453580.7946 (29-Jul, 7:04 UT), the end of the caustic exit was not reached yet. Our recent data is in agreement with previous binary-lens models with moderate mass ratios, but appear to be in conflict with our planetary models. However, the dense observations towards the end of the caustic exit provide a good opportunity for studies about the atmosphere of the source star.
As pointed out in PLANET anomaly update 2005 #10-3 (issued 28-Jul, 18:05 UT), the observed rise in OGLE 2005-BLG-327 steepened significantly over the previous 1.5 days, reaching about 0.7 mag/day, and latest Tasmanian data from the most recent night initially show a continuation of this trend, followed by a flattening. This suggests the suspected caustic exit being in progress and the associated peak being reached. A first exploration of parameter space (by D. Kubas) revealed the possibility that the observed anomaly results from a jovian planet orbiting the lens star, while there is a roughly similar probability for a more moderate mass ratio between the components of the considered binary lens. Continued monitoring of the event is necessary in order to confirm or reject the hypothesis of a planet and for being able to put tight constraints on its properties (should it exist).
After the high-magnification level in OGLE 2005-BLG-327 was retained for more than 3 days, PLANET anomaly update 2005 #10-2 (issued 26-Jul, 8:55 UT) reported a rise by about 0.15 mag over 8 hrs seen in PLANET data taken during the most recent night with the Danish 1.54m at ESO LaSilla (Chile). This could be the indication of a caustic exit being in progress or shortly to come.
As stated in PLANET anomaly update 2005 #9-2 (issued 23-Jul, 7:50 UT), PLANET data on OGLE 2005-BLG-226 collected with the Canopus 1.0m near Hobart (Tasmania) and the SAAO 1.0m at Sutherland (South Africa) show that there is a slope discontinuity in the light curve of OGLE 2005-BLG-226 near HJD=2453574.26 (22-Jul, 18:15 UT), where a steep decrease changes to a rather flat behaviour, indicating a caustic exit along our predictions.
In PLANET anomaly update 2005 #10-1 (issued 23-Jul, 8:20 UT), we reported that PLANET data taken with the SAAO 1.0m at Sutherland (South Africa) and the Danish 1.54m at ESO LaSilla (Chile) show that the light curve of OGLE 2005-BLG-327 remained roughly flat between HJD=2453574.252 (22-Jul, 18:03 UT) and HJD=2453574.695 (23-Jul, 4:41 UT) at a level about 0.1 mag fainter than the points collected the previous night, which triggered our anomaly alert.
The observed rising part of the light curve of event OGLE 2005-BLG-226 let us expect a large peak magnification of A_0 ~ 20 or even more, resulting in a large sensitivity for picking up lens binarity, including the presence of planets around the lens star, or finite-source effects. As announced in PLANET anomaly alert 2005 #9 (issued 22-Jul, 3:25 UT), just in the vicinity of the expected peak, data collected with the Danish 1.54m at ESO LaSilla (Chile) show a rise by more than 1 mag with respect to a best-fitting single-lens point-source model, in agreement with a caustic entry near HJD=2453573.2 (21-Jul, 17:00 UT). A similar rise has been inpependently observed by OGLE, which triggered their early early-warning system (EEWS), resulting in a secondary alert being circulated. In PLANET anomaly update 2005 #9-1 (issued 22-Jul, 12:20 UT), we reported that PLANET data collected with the Danish 1.54m at ESO LaSilla (Chile) between HJD=2453573.523 (22-Jul, 0:33 UT) and HJD=2453573.807 (22-Jul, 7:22 UT), OGLE data extending this range to earlier epochs including HJD=2453573.473 (21-Jul, 23:21 UT), and PLANET data from the Perth 0.6m near Bickley (Western Australia) taken between HJD=2453573.939 (22-Jul, 10:32 UT) and HJD=2453574.006 (22-Jul, 12:08 UT) favour the finite source passing over several caustic lines at once (e.g. near a cusp) rather than the light curve being due a the caustic entering a single fold line. By estimating the source to have taken 9-15 hours from the caustic entry to the observed peak near HJD=2453573.75 (22-Jul, 6:00 UT), assuming rough symmetry in agreement with the most recent data, a caustic exit is expected between HJD=2453574.12 (22-Jul, 14:50 UT) and HJD=2453574.38 (22-Jul, 21:10 UT).
As reported in PLANET anomaly alert 2005 #10 (issued 22-Jul, 6:20 UT), data collected with the Danish 1.54m at ESO LaSilla (Chile) on OGLE 2005-BLG-327 show a slowly-varying magnification at a level of ~1.5 mag above previous single-lens point-source models. A likely interpretation of this is the finite source passing over a caustic created by a binary lens, where the latter was entered roughly between HJD=2453571.8 and HJD=2453572.3 (20-Jul, 7:00 to 19:00 UT). Independently, the OGLE collaboration alerted on the same behaviour seen in their data. A proper assessment of the nature of this event requires additional data.
A rereduction of PLANET data collected with the Danish 1.54m at ESO LaSilla(Chile) showed that the earlier suspected anomaly in event OGLE 2005-BLG-377 that was reported in PLANET anomaly alert 2005 #8 (issued 19-Jul, 8:45 UT) turned out not to exist, as stated in PLANET anomaly update 2005 #8-1 (issued 20-Jul, 5:55 UT).
As PLANET anomaly alert 2005 #8 (issued 19-Jul, 8:45 UT) states, PLANET data taken with the Danish 1.54m at ESO LaSilla (Chile) indicate that OGLE 2005-BLG-377 has reached a peak with magnification A_0 ~ 23 near HJD=2453569.8 (18-Jul, 7:00 UT), and has started to rise again since HJD=2453570.6 (19-Jul, 2:30 UT), where we believe to see a brightening by about 0.5 mag until HJD=2453570.70 (19-Jul, 4:50 UT). The current data do not allow to draw a definite conclusion on the nature of the event. Amongst several possibilities, a planetary origin of the seen deviation might provide a reasonable explanation. The behaviour of this event is shown in the light curve and our data themselves are available from the list of monitored events.
In PLANET anomaly update 2005 #6-2 (issued 18-Jul, 0:05 UT), we reported that after an initial rise of about 0.3 mag observed on event OGLE 2005-BLG-331 between HJD=2453562.5 and HJD=2453565.5 (11-Jul until 14-Jul), PLANET data from the Canopus 1.0m near Hobart (Tasmania) and the Danish 1.54m at ESO LaSilla (Chile), in agreement with OGLE data, show the target to be approximately 1.2 mag fainter at the time of the alert. These data leave some room for one or two caustic exits between HJD=2453565.7 (14-Jul, 5:00 UT) and HJD=2453566.9 (15-Jul, 9:30 UT), when observations at several of our sites were prevented by bad weather.
Using our telescopes in Chile and Australia, we observed the caustic exit of OGLE 2005-BLG-153 / MOA 2005-BLG-23. The final exit of the source star from the caustic occurred at HJD=2453561.724 +/- 0.002 (10 Jul, 05:30 UT). This was announced in PLANET anomaly update 2005 #7-4 (issued 10-Jul, 07:25 UT).
As announced in PLANET anomaly update 2005 #7-3 (issued 9-Jul, 12:15 UT), continued monitoring of OGLE 2005-BLG-153 / MOA 2005-BLG-23 reveals that the anticipated caustic exit peak has been passed around HJD=2453460.4 (8-Jul, 21:30 UT), and the source is expected to leave to caustic at HJD=2453561.72 +/- 0.03 (10-Jul, 5:15 UT) after it needed (1.63 +/- 0.03) days for crossing it.
PLANET anomaly update 2005 #7-2 (issued 8-Jul, 9:15 UT) reports an observed rise to an expected caustic peak in OGLE 2005-BLG-153 / MOA 2005-BLG-23 with the source likely to start exiting within the next 24 hours.
After further OGLE data started to show a separate rise in OGLE 2005-BLG-331 after the suspected fold-caustic entry, which was initially expected to be related to the corresponding exit, subsequent observations by PLANET with the Danish 1.54m at ESO LaSilla as well as by OGLE reveal another fold-caustic entry happening before a caustic exit related to the first entry was observed. This was reported in PLANET anomaly update 2005 #6-1 (issued 4-Jul, 4:45 UT). Possible interpretations for the observed data could be a source binary passing behind a binary lens or a triple lens system.
Further PLANET observations on OGLE 2005-BLG-153 / MOA 2005-BLG-23 with the Danish 1.54m at ESO LaSilla support the detection of a caustic entry and show it to be still in progress, as reported in PLANET anomaly update 2005 #7-1 (issued 4-Jul, 11:50 UT). A fold-caustic approximation suggests the caustic entry to to have started around HJD=245355.97 (3-Jul, 11:10 UT) and to last about 1.8 days. The long duration together with the bright target makes this event another excellent candidate for studying a stellar atmosphere. For providing such information, both the beginning and the end of a caustic passage (entry or exit), corresponding to either the leading or the trailing limb passing, are of particular value. From the actual data, the source is expected to complete its caustic entry by HJD=2453556.8 (5-Jul, 6:30 UT), provided the model approximations are valid.
While OGLE data taken during earlier stages of the event OGLE 2005-BLG-153 / MOA 2005-BLG-23 already revealed anomalous behaviour by showing a further rise after the light curve had already flattened, PLANET data collected with the Canopus 1.0m near Hobart (Tasmania) suggest a caustic entry, as announced in PLANET anomaly alert 2005 #7 (issued 3-Jul, 18:15 UT). The reported features can be seen in our light curve showing the latest data, which is available from links within our list of monitored events.
On event OGLE 2005-BLG-331, the OGLE team reported a sudden strong rise in magnification exceeding 1 mag/hr and considered the possibility that they have caught a caustic entry in progress. By issuing a secondary alert, they enabled us to obtain data on this event during the same night with the Danish 1.54m at ESO LaSilla. As reported in PLANET anomaly alert 2005 #6 (issued 2-Jul, 11:55 UT), these data confirm the rise and together with more OGLE data support the interpretation of a fold-caustic entry. However, our data can only serve as an indication since we were not able to obtain a good reference frame yet and the weather conditions were far from optimal. A fold-caustic entry model would prefer a caustic passage time of (6 +/- 2) hrs, with the leading limb entering at HJD=2453553.712 +/- 0.003 (2-Jul, 5:05 UT). This would mean that the caustic passage is about to finish as the PLANET alert was circulated, with the trailing limb entering. In addition to the entry of the leading limb, this is a second phase of strong value for the measurement of limb darkening. A light curve with the latest data as well as the data themselves is available from our list of monitored events.
Following an announcement made by OGLE that the event OGLE 2005-BLG-333 was about to rise to a very high peak magnification, PLANET obtained data with the Canopus 1.0m near Hobart (Tasmania) showing that a peak at A_0 ∼ 60 occured around HJD=2453551.16 (29-Jun, 15:50 UT), which was reported in PLANET anomaly alert 2005 #5 (issued 29-Jun, 21:40 UT). Rather than strong finite-source effects, these data indicate an anomalous deviation lasting a few hours that might be attributed to the presence of a low-mass planet surrounding the lens star. However, a definitive claim requires a check of our preliminary on-line reduction along with proper modelling. A light curve showing the latest data as well as the data themselves can be obtained from links in our list of monitored events.
In PLANET anomaly update 2005 #4-1 (issued 21-Jun, 12:50 UT), we reported that the suspected early decrease in OGLE 2005-BLG-128 on 19-Jun has been contradicted by OGLE data collected later that night, which show that the event was still rising. While a single point from OGLE at HJD=2453541.6211 (20-Jun, 2:54 UT) indicates that the caustic peak has been passed, the flat behaviour of the light curve after HJD=2453541.7849 (20-Jun, 6:50 UT), revealed by PLANET data taken with the Danish 1.54m at ESO LaSilla, clearly shows that the source has exited the caustic. Another data point from the same site at HJD=2453542.7089 (21-Jun, 5:01 UT) suggests that the light curve remained flat since. OGLE and PLANET data collected on this event constrain the caustic exit to have lasted < 18 h. Further monitoring of the event will help to constrain the binary nature of the lens.
After OGLE data indicated that a fold caustic, created by a binary lens, had been entered by the source star in event OGLE 2005-BLG-128 between 25-Apr and 4-May, and a rise to the corresponding caustic exit peak had been observed, the OGLE team predicted a subsequent caustic exit to occur on 18-Jun. As reported in PLANET anomaly alert 2005 #4 (issued 19-Jun, 6:40 UT), PLANET data collected with the Danish 1.54m at LaSilla between HJD=2453540.6105 (19-Jun, 2:39 UT) and HJD=2453540.6701 (19-Jun, 4:05 UT) show a decrease by about 0.5 mag/hour and, together with earlier OGLE data, indicate the trailing limb of the caustic exit to occur at HJD=2453540.99 -0.11 +0.44 (19-Jun, 11:50 UT) after a caustic passage time of (18 -3 +11) hrs. While the data yield a reasonable picture, these conclusions crucially depend on each of just two measurements, which might be affected by systematic offsets that cannot be properly assessed at the moment. In order to observe chromatic effects in the light curve and quantify limb darkening of the source star, dense sampling is required over the falling part of the caustic exit peak until the source star has exited. Our regularly updated light curve shows current data along with a model. It can also be accessed via our list of monitored events, from which the data can also be retrieved in tabulated form.
In PLANET anomaly update 2005 #0-9 (issued 13-Jun, 11:10 UT), we reported that the final caustic exit in OGLE 2005-BLG-018 likely occured between HJD=2453531.90 (10-Jun, 9:30 UT) and HJD=2453532.00 (10-Jun, 12:00 UT). Our models predict the light curve to decrease monotonically until reaching baseline. No further rise is expected.
With the second caustic passage being in progress, PLANET anomaly update 2005 #0-8 (issued 5-Jun, 14:30 UT) reported that an updated model predicts the light curve to reach a peak around HJD=2453528.93 (7-Jun, 10:20 UT) and then fall at an increasing rate until the trailing limb of the source exits the caustic at about HJD=2453531.88 (10-Jun, 9:05 UT). Observations around an expected inflection point near HJD=2453527.90 (6-Jun, 9:35 UT) can be even more valuable for measuring the stellar brightness profile near the limb than those in the vicinity of caustic entries or exits.
In PLANET anomaly update 2005 #0-7 (issued 3-Jun, 01:00 UT) we reported the re-entry of the OGLE 2005-BLG-018 source into the caustic soon after HJD=2453523.8 (2-Jun, 07:12 UT), based on PLANET data from the Canopus 1.0m and the Danish 1.5m telescopes, as well as OGLE data. The event is now rising at around 0.3 mag per day, as shown by additional Canopus, Danish, and OGLE data since the alert. The caustic passage is expected to last around 7 days.
We reported in PLANET anomaly update 2005 #0-6 (issued 1-Jun, 9:15 UT) that PLANET data taken with the Danish 1.54m at ESO LaSilla, the Perth 0.6m and the Canopus 1.0m near Hobart, in agreement with OGLE data indicate that the source has exited the caustic before HJD=2453516.664 (26-May, 3:57 UT) and remained outside until that time. For a proper interpretation of the light curve, both the annual parallax resulting from the revolution of the Earth around the Sun, and the orbital motion of the stellar binary comprising the lens have to be taken into account. Since both of these effects can locally cause similar deviations, it is not easy to find their true combination, resulting in some uncertainty for the prediction of the expected re-entry of the source into the caustic. However, our models reveal a preferred time range for the caustic re-entry of HJD=2453523.4 +/- 0.1 (1-Jun, 19:00 - 24:00 UT). A precise determination of this epoch by collected data would provide strong constraints for the model parameters, while observations shortly after the caustic entry are highly sensitive to the brightness profile of the stellar limb.
On 12-Jan 2005, NASA has successfully lauched its Deep Impact spacecraft which is on its way to comet 9P/Tempel-1, which it is to hit on 4-July. This will provide the first look inside a comet with the aim to find clues to the origins of life in our Solar System. With its network of telescopes and its experience in regular monitoring, PLANET is well-suited in providing images of the comet on a daily basis. Being part of a world-wide campaign, coordinated by Karen Meech, such images will allow to study the evolution of the properties of the comet before, during, and after the impact.
Further PLANET data on OGLE 2005-BLG-018 taken with the Perth 0.6m from HJD=2453513.0986 (22-May, 14:22 UT) to HJD=2453513.2982 (22-May, 19:09 UT) and from HJD=2453514.1307 (23-May, 15:08 UT) to HJD=2453514.3640 (23-May, 20:44 UT) reveal a stronger decrease in magnitude than our simple model predicted. However, as pointed out in PLANET anomaly update 2005 #0-5 (issued 25-May, 10:20 UT), a parallax-included model provides a reasonable fit to both the caustic peak region and the first peak. Although Perth data were not included (in a first fit), they match the revised model prediction almost perfectly. This model predicts the source to exit the caustic near HJD=2453516.12 (25-May, 14:55 UT) and re-enter near HJD=2453520.73 (30-May, 5:30 UT) before finally exiting around HJD=2453530.56 (9-Jun, 1:26 UT). With the source moving under a small angle with respect to the caustic tangent, the epoch of caustic re-entry is difficult to estimate and therefore subject to refinement as further data has been obtained. A small shortcoming around the first peak should be resolved by lens orbital motion which has been found to play a smaller role than parallax from the data. However, this might also affect the future predicted behaviour a bit. The data point taken at the Danish 1.54m in the night of 24-May is strongly doubtful, thanks to the bright sky due to the moon. If this measurement is correct however, it would point to an earlier caustic exit, which could have already taken place. The coming long-lasting caustic passage of about 1.5 weeks duration will provide an unprecedented opportunity for resolving a stellar atmosphere, where current data already favour a linear limb-darkening coefficient of c ~ 0.62. The huge potential is linked to several favourable properties, namely the long event time-scale, the large angular source size as compared to the angular Einstein radius, the brightness of the source, the variety of caustic crossing angles, and the predictability.
Evidence for a low-mass companion to the lens star in OGLE 2005-BLG-071
PLANET has taken part in a common effort of several research teams with the goal to hunt down a suspected planet orbiting the lens star that gave rise to microlensing event OGLE 2005-BLG-071. After having been notified by μFUN about anomalous behaviour in the perspective high-magnification event, confirmed by OGLE, PLANET was able to activate part of its network ahead of the regular observing season, while PLANET's cooperative sites of UK-operated telescopes forming Robonet were already in operation. Moreover, MOA also succeeding in collecting data on this event. The light curve shows two sharp peaks, about 12 h wide, which are about 3 days apart. As first suggested by M. Jaroszynski, it can be well-explained by the distortion caused by a caustic located near the center of the lens star that results from the presence of a low-mass companion, where best-fit model parameters are a mass ratio of q ∼ 0.007 and a separation parameter of either d = 1.3 or d = 0.76, which denotes the angular instantaneous separation between planet and parent star in units of the angular Einstein radius &thetaE. The ambiguity in the separation is a general intrinsic feature. In contrast to the proposed planetary system, stellar binaries are unable to produce a light curve that is consistent with the observed data, and therefore do not provide an alternative interpretation. With the measured event time-scale tE ∼ 70 d, the assumption that the source is at a distance DL ∼ 8.5 kpc, and models for the Galactic disk and bulge populations, we conclude that we have likely detected a planet with mass M ∼ 2.7 Mjup orbiting a lens star with mass M ∼ 0.45 Msun located at DL = (5.2 ± 1.8) kpc, where the semi-major axis of the orbit is a ∼ 2.2 AU or a ∼ 3.7 AU, corresponding to an orbital period of P ∼ 5 yr or P ∼ 11 yr. More details are available in preprint astro-ph/0505451 of a letter submitted to The Astrophysical Journal. A more thoroughful and detailed analysis is underway with the aim to determine the uncertainties of the estimates of mass and and orbital axis in order to confirm the planetary nature of the detected companion.
It has turned out that the previously suggested flattening in OGLE 2005-BLG-018 resulted from a misalignment between observing sites and that the event continued to rise instead. In PLANET anomaly update 2005 #0-4 (issued 23-May, 16:25 UT), we reported that a model arising from just placing a finite source on top of our most recent point-source model provides a reasonable fit of the caustic entry as well as all data collected by PLANET with the Canopus 1.0m near Hobart and the Danish 1.54m at ESO LaSilla and by OGLE during the caustic passage between HJD=2453511.1937 (20-May, 16:39 UT) and HJD=3512.9325 (22-May, 10:23 UT), where the first data point arises from the Canopus 1.0m and the most recent one from OGLE, who also took the last data point before the caustic entry. Despite the success of our model in the region of the caustic passage, it fails on reproducing the first peak, which could be attributed to the negligence of both the orbital motion of the binary lens and the annual parallax caused by the revolution of the Earth. While we will try to resolve this, we expect that it will affect the light curve over the next 10-14 days much less than it did since the first peak (that occured around 31-Mar, 7.5 weeks ago). Unfortunately, we currently lack of more recent data that could confirm the model, contradict it, or yield further constraints. If our model is right, the caustic peak is strongly skewed, hanging towards later epochs, and the maximum was reached at HJD=2453512.85 (22-May, 8:25 UT) with 3.9 mag above baseline. We expect a current magnification of 3.3 mag and a decrease with the rather constant rate of 0.45 mag/day until about HJD=245315.5 (25-May, 0:00 UT), where the light curve starts flattening until reaching a minimum near HJD=2453518.2 (27-May, 17:00 UT) at 2.1 mag above baseline.
As reported in PLANET anomaly alert 2005 #3 (issued 22-May, 8:50 UT), rather than the expected rise to the peak expected to be reached within a short time, PLANET data on OGLE 2005-BLG-216 collected with the Danish 1.54m at ESO LaSilla between HJD=2453512.6573 (22-May, 3:46 UT) and HJD=2453512.8364 (22-May, 8:04 UT) indicate a decrease by about 0.15 mag that is incompatible with models assuming point-like sources and lenses. The OGLE collaboration suggests that the event is substantially blended, pushing the source magnification at a much larger value than the observed A ~ 10. OGLE data however does not support an anomaly being in progress.
In PLANET anomaly update 2005 #0-2 (issued 21-May, 8:10 UT), we reported that PLANET data collected on OGLE 2005-BLG-018 with the Canopus 1.0m near Hobart show that the expected cusp passage started around HJD=2453511.1 (20-May, 14:30 UT). Data obtained with the Danish 1.54m at ESO LaSilla taken from HJD=2453511.628 (21-May, 3:05 UT) confirm this interpretation and show that the passage is in progress, where it still might take up to 24 hrs until the peak is reached, roughly in agreement with the prediction of our latest model for a point-like source calculated before the caustic passage started. Prior to our update, OGLE had issued a secondary alert reporting the anomaly being in progress. As announced in PLANET anomaly update 2005 #0-3 (issued 21-May, 13:45 UT), PLANET data taken with the Canopus 1.0m near Hobart between HJD=2453512.016 (21-May, 12:23 UT) and HJD=2453512.023 (21-May, 12:33 UT) suggest a flattening in the light curve compared to the rise observed in earlier data collected by PLANET with the Danish 1.54m at ESO LaSilla and by OGLE, where the OGLE data was particularly useful for us for properly aligning the Danish data in magnitude. The flattening suggests that the event was around peak at the time when the anomaly update was circulated. If this interpretation is correct, it would imply a passage duration of ∼ 1.8 days, so that the caustic will be exited at about HJD=2453513.95 (23-May, 11:00 UT). With the assessment of the source size during the caustic passage, the accurate predication of the fold-caustic entry will become possible. A good coverage of all the distinctive features will then allow a reliable determination of the characteristics of the underlying binary lens. We plan to update our prediction as more data is collected. Current data and model are show on our regularly updated light curve, which can also be accessed via our list of monitored events, from which you can also retrieve the data in tabulated form.
After data collected by OGLE, MOA, PLANET/RoboNet and MicroFUN indicated that event OGLE 2005-BLG-158 / MOA 2005-BLG-17 would peak at a magnification in excess of 50, assuming a point-like source, the monitoring of this event has been intensified, since finite-source effects as well as lens binarity could be expected to show up. While the observation of finite-source effects provides the opportunity to resolve the stellar atmosphere, events where the angular separation between lenses and sources becomes very small, resulting in very large peak magnifications, harbour a large potential for planets around the lens star to be revealed. As reported in PLANET anomaly alert 2005 #2 (issued 20-May, 7:15 UT), PLANET succeeded in obtaining data with the Danish 1.54m telescope between HJD=2453510.7526 (20-May, 6:04 UT) and HJD=2453510.7963 (20-May, 7:07 UT), despite bad weather at the site. These data show that the event was near peak at a magnification of about 90, while further monitoring still being in progress. After the observations at the Danish 1.54m terminated for the night at HJD=2453510.9321 (20-May, 10:22 UT), we reported in PLANET anomaly update 2005 #2-1 (issued 20-May, 14:40 UT) that the light curve near the peak showed a flattening that indicates finite-source effects. The same behaviour is independently confirmed by OGLE data covering a similar time range. From a simple finite-source model (that needs some refinement), we estimate that the source moves by its radius in about 9 hours relative to the lens. With the source being a clump giant with angular radius ~ 5.7 μas (A. Gould, private communication), this implies a relative proper motion of ~ 15 μas/day. More information about the nature of the event will result from PLANET data taken before the peak with the Canopus 1.0m near Hobart. The finite-source model is displayed on our light curve, while a data table can be retrieved from our list of monitored events.
Data on OGLE 2005-BLG-018 collected by OGLE and PLANET/Robonet with the Danish 1.54m at ESO LaSilla and the Faulkes North 2.0m after circulation of PLANET anomaly alert 2005 #0 (issued 9-May, 23:15 UT) has been used to refine our models. As pointed out in PLANET anomaly update #0-1 (issued 18-May, 18:10 UT), we now believe that it is likely that the source is on the approach to a cusp until HJD=2453513.9 (23-May, 9:30 UT) before it enters a fold caustic at around on HJD=2453526.66 (5-June, 3:50 UT), which is exited about 3 days later. This prediction is based on the assumption of a point-like source. An assessment of the source size during the caustic passage could allow the accurate predication of the fold-caustic entry. With a good coverage of all the distinctive features, the characteristics of the underlying binary lens will be well-determined. During the course of this event, we will regularly update our models and provide a light curve showing recent data. Moreover, you can now retrieve the data in tabulated form from our list of monitored events.
As of today, PLANET will be in full operation for its 2005 observing season, during which it is our aim to provide the astronomical community with frequently updated information about ongoing microlensing events in the form of light curve plots and data tables. The provision of data tables will start as soon as the remaining technical obstacles are overcome. For (suspected) anomalies, PLANET Anomaly Alerts and Updates will be issued, which summarize the observations and include (if possible) an explanation of their likely nature as well as a prediction of the future behaviour of the event.PLANET Anomaly Alerts and Updates are circulated to everyone who requests to be added to our mailing list. The success of PLANET depends on the number and quality of the microlensing alerts issued by OGLE and MOA. We strongly appreciate their work and we are particularly pleased that they make preliminary versions of their reduced data available in near-real time. Moreover, preliminary data made available by MicroFUN as well as alerts on anomalous behaviour received by them, have shown to be helpful for us in scheduling the observations and deriving suitable models. With the 2005 observing season, PLANET is to join forces for a microlensing campaign with RoboNet-1.0, a network of three UK-operated 2.0m robotic telescopes.
As pointed out in PLANET anomaly alert 2005 #0 (issued 9-May, 23:15 UT), OGLE data on event OGLE 2005-BLG-018 revealed a first peak around HJD=2453461 (31-Mar), with a half-maximum width of about 8 d, after whichthe event rose again and is still rising as the alert was issued, indicated by both OGLE and PLANET/RoboNet data collected at the Faulkes North 2.0m telescope. Preliminary models indicate the lens to be a stellar binary with a mass ratio in the range q ∼ 0.7–1.0, where this is however quite uncertain. If this interpretation is approximately correct, a fold-caustic entry will occur within the subsequent 10 days. The event time-scale of t_E ~ 55 days would allow a dense coverage of both the fold-caustic entry and the fold-caustic exit if accurately predicted, enabling not only a precision measurement of the stellar brightness profile, but also an accurate determination of the parameters of the binary lens. There might also be the potential for detecting parallax effects, which, together with the measurement of the proper motion between lens and source star obtained from finite-source effects, would provide a measurement of the mass of the lens constituents. We plan to update our prediction as more data is collected. Current data is shown on the light curve.
A paper about the determination of the lens mass and distance of the binary lens that caused the event OGLE 2002-BLG-069 has been accepted for publication in A&A (Kubas et al. 2005), which is available as preprint astro-ph/0502018. This event involves a pair of fold-caustic passages which produce characteristic peaks of well-defined shape. With its 2002 season telescope network, PLANET managed not only to obtain a good coverage of the caustic exit, but also of a fair part of the caustic entry. With the physical size of the source star and the source distance being well-determined by high-resolution spectra from UVES at the VLT (Paranal, Chile), the observation of the caustic passage duration and of effects caused by the Earth's orbital motion yield a total lens mass M = (0.51 ± 0.15) Msun for a mass ratio q = 0.58 and a lens distance DL = (2.9 ± 0.4) kpc for a close-binary lens model, in agreement with the observed blend ratio. In contrast, a wide-binary lens model that is in agreement with the photometric data yields a mass M ≥ (126 ± 22) Msun and a distance DL ≥ (9.0 ± 2.3) kpc, which is in contradiction with the lens being dark, unless one assumes an unlikely black-hole binary. More information can also be found in our news report.
By quantitatively assessing the effects of the extent of the source star and the annual parallax seen in the photometric light curve of OGLE 2003-BLG-238, the combined efforts by the OGLE, PLANET, and MicroFUN collaborations with the 1.3m Warsaw telescope at Las Campanas Observatory (Chile), the CTIO 1.3m at Cerro Tololo (Chile), the Wise 1.0m at Mitzpe Ramon (Israel), the Danish 1.54m at ESO La Silla (Chile) and the Canopus 1.0m near Hobart (Tasmania) not only allowed to measure the event timescale tE = (37.6 ± 0.2) d and the angular Einstein radius &thetaE = (652 ± 56) μas, but also revealed a 1-σ constraint on the parallax, given by 0.056 < πLS/&thetaE < 0.23, so that the lens mass is constrained to 0.36 Msun < M < 1.48 Msun. Although a measurement of the lens mass by this technique is complicated by the fact that those events that are most likely to show prominent finite source effects are the least likely to show prominent parallax effects, vice versa, the data allowed to obtain a meaningful constraint for an event with a relative proper motion between lens and source of μ ∼ 6 mas/yr, which is rather typical for disk lenses. While OGLE 2003-BLG-238 shows the general feasibility of this approach, events with smaller proper motions will provide better opportunities. Read more about this in our news report or in the preprint astro-ph/0404394 of our corresponding paper, now accepted for publication in The Astrophysical Journal (Jiang et al. 2004).
With 31-Aug, PLANET has completed its regular observations for the 2004 season. Prime events may still be monitored on the opportunity.
PLANET anomaly update #15-3 (issued 20-Aug, 7:30 UT) reports that PLANET data reveal that the caustic passage of OGLE 2004-BLG-482 lasted from HJD = 2453234.57 (17-Aug, 1:45 UT) until HJD = 2453237.01 (19-Aug, 12:15 UT), so that it took about 2.44 days from the caustic entry of the leading limb of the source until the caustic exit of its trailing limb.
Our broad-band photometric measurements on OGLE 2004-BLG-482 are complemented by high-resolution spectra obtained with the UVES spectrograph at the VLT Kueyen telescope located at ESO Paranal (Chile) during the nights of 17-Aug and 18-Aug. Making use of our previously awarded target-of-opportunity status, in total 16 spectra have been taken in the night of 17-Aug during 6 consecutive hours alternating between the two instrumental setups 580 and 860, thereby covering a spectral range of 4500-10800 Å at λ/(Δλ) ∼ 40,000. During the night of 18-Aug, we got 4 spectra taken from 4:35 UT when the lens was at a fractional radius of 0.80, where strong signatures due to differential magnification of different parts of the source can be expected as the lens transits its limb. The latter observations were only possible thanks to the visiting astronomers C. De Breuck and B. Rocca Volmerange kindly accepting that our target-of-opportunity observations would take place in order to catch this unique opportunity. In order to obtain reference spectra, subsequent post-caustic spectral observations are planned for the night of 20-Aug or 21-Aug.
Latest PLANET data from LaSilla and Hobart confirm our earlier interpretation that the OGLE 2004-BLG-482 source has entered a caustic. The event is currently close to its peak at a magnification of about 3 mag above baseline. We continue our effort of dense photometric and multiband /spectroscopic measurements and to catch the caustic exit of the trailing limb expected to occur around PHD=3236.95. Please see our regularly updated lightcurve for the latest developments and PLANET anomaly update #15-2 (issued 18-Aug, 9:30 UT).
As announced in PLANET anomaly update #15-1 (issued 17-Aug, 13:30 UT) latest PLANET observations on OGLE 2004-BLG-482 from Chile and Tasmania indicate that the source, likely to be an M5III giant, has entered a caustic and is about to leave it within the next 12-24 hours.
PLANET observations on OGLE 2004-BLG-482 with the Canopus 1.0m telescope near Hobart (Tasmania, Australia) from the last two nights show a rise to a magnification of about 2 mag above baseline and indicate that a peak will occur within the following 24-48 hours at a very high magnification, which might exceed A0 ∼ 100, as pointed out in PLANET anomaly alert #15 (issued 16-Aug, 16:05 UT). Despite the extraordinary potential for detecting extra-solar planets in this event, finite source effects may show up in the lightcurve (allowing a measurement of the relative proper motion between lens and source). Moreover, the brightness of this target (already I = 14.1 at baseline) makes this target a good candidate for multi-band and spectroscopic measurements. Please see our regularly updated lightcurve for the latest developments.
Continued observations on OGLE 2004-BLG-347 as reported in PLANET anomaly update 2004 #14-1 (issued 6-Aug, 7:45 UT) carried out by PLANET with the 1.54m Danish telescope at ESO LaSilla (Chile), the Canopus 1.0m telescope near Hobart (Tasmania, Australia), and the Perth 0.6m telescope at Bickley (Western Australia) reveal a smooth second peak around HJD = 2453219.5 +/- 0.5 (2-Aug, 0:00 UT +/- 12 h) with a magnification of about 1.25 mag above baseline in agreement with OGLE data taken over the same period. The event is expected to approach a light curve roughly consistent with that of point-like sources and lenses over the next few days. In general, lightcurves with two smooth peaks as observed in this event are compatible with a stellar binary lens or a binary source. A closer analysis will show which of these interpretations is the more likely. A regularly updated lightcurve showing PLANET and OGLE data presents the most recent developments.
After previous OGLE and PLANET data on event OGLE 2004-BLG-347 have shown a first peak around HJD = 2453207.6 +/- 0.2 (21-Jul, 1:30 UT +/- 4 h) at about 1.05 mag above baseline and a slight decrease by about 0.05 mag until HJD = 2453212.0 +/- 0.5 (25-Jul, 12:00 UT +/- 12 h), recent data collected by PLANET with the 1.54m Danish telescope at ESO LaSilla (Chile) show another increase by 0.15 mag until HJD = 2453217.73 (31-Jul, 5:30 UT) as reported in PLANET anomaly alert 2004 #14 (issued 31-Jul, 8:05 UT). It is suggested that the lens is a binary. We might approach a cusp caustic or a fold-caustic exit (where the entry has been missed and the observed minimum marks the trough between the two caustic passages). Future observations will help to reveal the true nature of this event. The progress of this event can be seen on our regularly updated lightcurve.
Data observed by PLANET on OGLE 2004-BLG-441 with the SAAO 1.0m telescope at Sutherland (South Africa), the Canopus 1.0m telescope near Hobart (Tasmania, Australia), and the Danish 1.54m telescope at ESO LaSilla (Chile) in three consecutive nights beginning 21-Jul show a departure from a lightcurve compatible with point-like source and lens near the peak at HJD = 2453208.52 +/- 0.05 (22-Jul, 0:30 UT +/- 12 h) with a magnification of about 1.8 mag above baseline. If this deviation is due to the finite source size rather than binarity, our observations would allow us to measure the relative proper motion between lens and source, and with a determination of parallax, we would obtain mass and distance of the lens. The described anomaly can be seen in our lightcurve showing PLANET and OGLE data.
As reported in PLANET anomaly update 2004 #13-1 (issued 26-Jul, 14:20 UT), dense observations over the course of the caustic exit of event OGLE 2004-BLG-309 carried out by PLANET with the SAAO 1.0m telescope at Sutherland (South Africa) between HJD = 2453206.226 (19-Jul, 17:25 UT) and HJD = 2453206.514 (19-Jul, 0:20 UT) will provide not only a precise measurement of the relative proper motion between lens and source, which will constrain lens mass and distance, but also show a strong signal of limb darkening. After the caustic exit peak, the event faded by about 2.4 mag until the trailing limb of the source exited at HJD = 2453206.441 +/- 0.007 (19-Jul, 22:35 UT +/- 10 min), depending on the assumed amount of limb darkening which might be quite substantial and smoothen the light curve at this epoch. Subsequently, the event brightened again by about 0.8 mag until a peak around HJD = 2453209.3 +/- 0.15 (22-Jul, 19:00 UT +/- 4 h) after which the observed luminosity is expected to approach a Paczynski-curve asymptotically. Most recent developments can be seen in our regularly updated lightcurve.
After having already observed and reduced data for PLANET during his MSc studies, Christian Vinter (Niels Bohr Institute, University of Copenhagen, Denmark) has now become full member of the PLANET collaboration.
PLANET anomaly alert 2004 #13 (issued 19-Jul, 23:13 UT) reported a caustic exit in progress on event OGLE 2004-BLG-309, where the corresponding peak occured at HJD = 2453206.31 +/- 0.01 (19-Jul, 19:26 UT +/- 15 min) at a magnification of ~ 2.8 mag above baseline as could be seen from ongoing observations at the SAAO 1.0m at Sutherland (South Africa).
From Friday, 16-Jul until Monday, 19-Jul, PLANET was able to take data on three caustic exits, occuring on events OGLE 2004-BLG-373, OGLE 2004-BLG-379, and OGLE 2004-BLG-409. Regular dense observations on a significant number of these provides the basis for measurements of stellar limb-darkening coefficients and further studies of stellar atmospheres which result from observing a temporal sequence of high-resoultion spectra. Besides hunting for extra-solar planets, this forms an integral part of the core science of PLANET.
As reported in PLANET anomaly alert 2004 #12 (issued 17-Jul, 21:35 UT), a few data points collected by PLANET the same day on OGLE 2004-BLG-379 with the Canopus 1.0m telescope at Hobart (Tasmania) and the Perth Observatory 0.6m telescope at Bickley (Western Australia) indicate that a caustic exit has occured with a peak magnification at HJD = 2453204.05 +/- 0.05, from whence it has fallen in brightness by ∼ 3-4 mag to the exit of the trailing limb at HJD = 2453204.25 +/- 0.05. PLANET and OGLE data for this event are displayed on our regularly updated lightcurve.
As reported in PLANET anomaly update 2004 #11-1 (issued 16-Jul, 7:20 UT), further data on OGLE 2004-BLG-373 collected by PLANET over the night beginning on 15-Jul with the Danish 1.54m telescope at ESO LaSilla and the SAAO 1.0m telescope at Sutherland (South Africa) show that the caustic exit has not occured yet. An observed brightening by about 0.5 mag over the trough between the caustic passages now indicates that the center of the source is likely to exit at HJD = 2453203.41 (-0.21/+0.25), i.e. 16-Jul, 21:50 UT (-5 h/+6 h).Data collected by PLANET with the Perth 0.6m at Bickley (Western Australia) and the SAAO 1.0m telescope at Sutherland (South Africa) show that OGLE 2004-BLG-373 finally underwent the expected caustic exit, where the centre of the source exited at HJD = 2453203.15 +/- 0.05 and the trailing limb at HJD = 2453203.2525 +/- 0.0.0025. During this time the brightness decreased by approximately 2 magnitudes, as reported in PLANET anomaly update 2004 #11-2 (issued 16-Jul, 23:30 UT). These observations allow a reliable measurement of the proper motion between lens and source, which can be used to constrain the lens mass and distance, whereas limb-darkening are only marginally detected with the obtained coverage during the caustic passage which lasted only about 5 hours. For your information, we continue to provide a regularly updated lightcurve.
As reported in PLANET anomaly alert 2004 #11 (issued 15-Jul, 8:30 UT), recent data collected by PLANET with the Danish 1.54m telescope at ESO LaSilla (Chile) on the event OGLE 2004-BLG-373 indicates that a caustic exit may be ongoing with the source center passing the caustic at HJD=2453201.8474 (15-Jul, 8:20 UT). However, this estimate is strongly biased by a single data point and the expected caustic exit may happen only in a few days time. A dense coverage is strongly urged in order not to miss this anomaly or repredict the time of the caustic exit. Caustic exits harbour the potential for obtaining measurements of the proper motion between lens and source stars and the brightness profile of the source. With a good photometric coverage, uncertainties in the properties of the underlying binary lens system are strongly reduced and if parallax effects can be assessedp roperly, even a lens mass measurement is possible. A currently updated lightcurve is provided.
PLANET anomaly update 2004 #10-3 (issued 5-Jul, 8:30 UT) reports that reduction of data collected by PLANET on OGLE 2004-BLG-368 with the Canopus 1.0m telescope near Hobart (Tasmania, Australia) during the two consecutive nights starting on 28-Jun and 29-Jun reveal additional important information about the observed caustic passage. Two points on the rise following the observed caustic entry at HJD=2453184.75 +/- 0.01 (28-Jun, 6:00 UT +/- 15 min) indicate a peak around HJD=2453185.25 (28-Jun, 18:00 UT) at more than 3.5 mag above baseline, after which the event dropped to a magnification of 2.85 mag at HJD=2453185.55 (29-Jun, 1:10 UT) and rose again to a peak at 3.0 mag at HJD=2453185.65 (29-Jun, 3:35 UT). The Tasmanian data favour a slope dicontinuity marking the end of the caustic passage at HJD=2453186.13 +/- 0.01 (29-Jun, 15:07 UT +/- 15 min), so that the caustic passage lasted about 33 hours.
Further PLANET data collected on OGLE 2004-BLG-368 with the Danish 1.54m telescope at ESO LaSilla (Chile) from HJD=2453185.4 to HJD=2453186.7 (29-Jun, 2004) show that OGLE 2004-BLG-368 has exited a caustic and continues to decline, expected to approach an ordinary lightcurve. This has been reported in PLANET anomaly upda te 2004 #10-2 (issued 30-Jun, 9:40 UT). The lightcurve is compatible with a caustic entry around HJD=2453184.4 and a rise to a peak near HJD=2453185.2 (which is not covered by our data) followed by anot her close peak near HJD=2453185.7 (which is covered by our data) at roughly the same magnification of 3.0 mag above baseline, where the magnification drops only by about 0.15 mag in between these two peaks. The source is believed to have exited the caustic at HJD=2453186.15 +/- 0.05. The structure of the observed caustic passage is typical for events where the source center passes close to a cusp and the leading limb starts exiting before the trailing limb has entered.
As reported in PLANET anomaly alert 2004 #10 (issued 28-Jun, 23:55 UT), data collected on OGLE 2004-BLG-368 by PLANET with the Danish 1.54m telescope at ESO LaSilla (Chile) from HJD=2453184.5 to HJD=2453184.9 (28-Jun, 2004) and data taken by the MicroFUN collaboration independently suggest two peaks which are estimated to have occured at HJD=2453184.25 +/- 0.25 and at HJD=2453185.0 +/- 0.25 but were not observed themselves. One might speculate a bit about the nature of a suspected binary lens that could have caused this event and the corresponding trajectory. Based on the short time-scales involved, a small caustic related to a planetary companion may provide a viable explanation. Future observations are likely to lift the shadow on this.
With data from the Danish 1.54m telescope at ESO LaSilla (Chile) collected between HJD=2453185.4 and HJD=2453185.9 (28-Jun, 2004) having become available, PLANET anomaly update 2004 #10-1 (issued 29-Jun, 9:30 UT) was circulated. These data provide evidence that the event is still undergoing an anomaly. An apparent peak was observed at HJD 2453185.6 with a magnification of about 3 mag above baseline and the event has subsequently faded by 0.3 mag until the end of the night. One might speculate a bit about the nature of a suspected binary lens that could have caused this event and the corresponding trajectory. Based on the short time-scales involved, a small caustic related to a planetary companion may provide a viable explanation. Future observations are likely to lift the shadow on this. The second peak is probably associated with a caustic entry, where most recent data may be on the decrease from the corresponding peak or already be associated with a close caustic exit (where the source passes close to a cusp). A lightcurve with PLANET and OGLE data is regularly updated.
OGLE data on OGLE 2004-BLG-280 showed a peak near HJD=2453169 (12-Jun) at only ~ 0.3 mag above baseline which was followed by another rise from 0.2 mag to 0.4 mag above baseline between HJD=2453178 (21-Jun) and 2453183.8 (27-Jun, 7:10 UT). Subsequently, PLANET has been able to collect data with the Danish 1.54m telescope at ESO LaSilla (Chile) from HJD=2453184.549 (28-Jun, 1:10 UT) to HJD=2453184.889 (28-Jun, 9:20). We are currently not sure whether we can trust our preliminary data reduction, but if we do so, the most likely nature of the observed anomaly is a caustic entry around HJD=2453184.5 followed by a caustic exit around HJD=2453184.9, i.e. only about 10 hours (!) later. The source therefore might have crossed a small caustic associated with a planetary companion to the lens, but we consider other binary lens configurations also being possible. Since the seeing varied significantly during the course of our observations, we might at all be fooled although the size of deviations is larger than typical for being caused by such effects. The suspected anomaly being present in our data has been reported in PLANET anomaly alert 2004 #9 (issued 28-Jun, 15:35 UT). We also provide a regularly updated lightcurve showing OGLE and PLANET data.
Further PLANET data taken on MOA 2004-BLG-33 (OGLE 2004-BLG-367) at the Canopus 1m near Hobart (Tasmania, Australia) between HJD=2453181.06 (25-Jun, 16:05 UT) and 2453181.22 (24-Jun, 17:17 UT), showed a continuation of this slow decline, while data from the following night, taken between HJD=2453182.17 (25-Jun, 16:05 UT) and 2453182.29 (25-Jun, 18:58 UT) show a marked drop of 0.7 to 0.8 mag, and a change in slope to a faster decline. This has been reported in PLANET anomaly update 2004 #8-1 (issued 26-Jun, 4:00 UT).
Our paper (H. Ghosh et al., 2004), written in collaboration with MicroFun, OGLE, and MOA, on the potential for an accurate measurement of the mass of the lens that caused OGLE 2003-BLG-175 / MOA 2003-BLG-45 by future space-based astrometric observations has been accepted for publication in The Astrophysical Journal. Please click for more details or retrieve the corresponding preprint astro-ph/0405500.
On June-22, 16:36 UT, MOA issued an alert for the event MOA-2004-BLG-33 (also known as OGLE 2004-BLG-367), warning of extremely high magnification, with the peak due in 8 hours time. Subsequently, OGLE, MicroFun, MOA, and PLANET data showed a peak of around I=12.5 near HJD=2453179.6 (June 23.1), with a peak magnification of over 100. After the peak, OGLE and PLANET data show that the event seems to have reached a plateau around I=14.6 (all OGLE magnitudes). This could be a caustic entry caused by a binary lens, but the exact nature of the anomaly is unclear, and dense monitoring is recommended in PLANET anomaly alert 2004 #8 (issued 24-Jun, 10:45 UT).
After data collected by the OGLE collaboration on the event OGLE 2004-BLG-250 indicated that the source entered a fold caustic between HJD-2450000 = 3152.9 (27-May, 9:30 UT) and HJD-2450000 = 3153.8 (28-May, 7:10 UT) and a decrease to a rather flat plateau region in the lightcurve was observed, PLANET anomaly alert 2004 #7 (issued 17-Jun, 9:40 UT) reported that PLANET data collected with the Danish 1.54m telescope at ESO LaSilla (Chile) showed a rise by about 0.6 mag between HJD-2450000 = 3168.8 (12-Jun, 7:10 UT) and HJD-2450000 = 3173.7 (17-Jun, 4:50 UT), leading to the prediction that the source center was to pass the caustic at HJD-2450000 = 3176.08 (-0.55/+0.62), i.e. 19-Jun, 14:00 UT (-13 h/+15 h).
The caustic exit in OGLE 2004-BLG-250 appeared to be both short and sudden (i.e. it involved a short caustic rise time). As pointed out in PLANET anomaly update 2004 #7-1 (issued 17-Jun, 14:30 UT), OGLE data collected until 17-Jun, 8:36 UT together with PLANET data from the Danish 1.54m telescope at ESO LaSilla (Chile) until 17-Jun, 8:55 UT reveal that the expected caustic exit ended between HJD-2450000 = 3173.684 (17-Jun, 4:25 UT) and HJD-2450000 = 3173.747 (17-Jun, 5:55 UT). Despite the fact that most of the caustic exit was not covered by either of these data sets, the caustic passage duration can be restricted to be less than 16 hours. The previous estimate of the time of caustic exit was hampered by the wrong assumption that one of the data points was on the rise to the caustic exit peak, while it is now clear that it was observed during the decrease after the peak. A regularly updated lightcurve, showing data from PLANET, OGLE, and MicroFUN, is available.
PLANET anomaly update 2004 #5-3 (issued 10-Jun, 21:40 UT) reports that PLANET data collected on OGLE 2004-BLG-254 at the SAAO 1.0m at Sutherland (South Africa) reveal a sign change in curvature on Jun-10 at around 21:00 UT, roughly corresponding to the source exiting the caustic created by the lens star. Together with previously collected data, we find that the caustic transit of the source lasted about 26 hours, i.e. a bit less than previously estimated.
Data collected on OGLE 2004-BLG-274 by PLANET with the Danish 1.54m ESO LaSilla (Chile) and by OGLE after 11-Jun, 0:05 UT appeared to be inconsistent with a previous model of a point source and a point-like lens where blending has been neglected. Originally, PLANET issued PLANET anomaly alert 2004 #6 (issued 11-Jun, 12:10 UT) triggered by a suspected rapid rise by 0.5 mag within one hour, but this was retracted in PLANET anomaly update 2004 #6-1 (issued 11-Jun, 14:00 UT), where it was instead stated that for a strongly blended target, a peak at a magnification of A0 = 90 (-25/+88) at 12-Jun, 17:00 UT (-5 h/+3 h) can be expected. The high peak magnification (which will however be reduced by finite source effects) makes this event another prime target for detecting extra-solar planets and studying stellar atmospheres.
The observation of finite source effects in OGLE 2004-BLG-254 has been reported in PLANET anomaly update 2004 #5-1 (issued 10-Jun, 4:10 UT), which are apparent in PLANET data from the SAAO 1.0m at Sutherland (South Africa) after 9-Jun, 18:50 UT and subsequent data from the Danish 1.54m at ESO LaSilla (Chile) as well as in OGLE data. As reported in PLANET anomaly update 2004 #5-2 (issued 10-Jun, 12:45 UT), the first half of the source star passed the caustic created by the lens in about 16 hours and a peak has been observed on 10-Jun around 7:40 UT at 4.35 mag above baseline, i.e. at a magnification of ∼ 55. Continuing dense coverage will allow a measurement of limb darkening of the source star. A reliable measurement of the passage time and an assessment of parallax can moreover be used to determine the mass of the lens star.
Data collected by PLANET, OGLE, and MicroFUN on OGLE 2004-BLG-254 showed a rise in magnification by 2.85 mag above baseline until 9-Jun, 8:10 UT. Provided that source and lens can be approximated by point-like objects, these data indicate a peak to occur on 10-Jun, 6:35 UT -30 min +20 min at a rather uncertain, but in any case large, magnification of 80 -30 +70. Events of this type harbour an exceptional potential both for the discovery of of extra-solar planets as well as for the study of stellar atmospheres, and might provide an opportunity for measuring the mass of the lens star. This has been reported in PLANET anomaly alert 2004 #5 (issued 9-Jun, 20:50 UT).
As reported in PLANET anomaly update 2004 #3-2 (issued 6-Jun, 15:35 UT), OGLE 2004-BLG-273 brightened by ∼ 1.2 mag since the caustic exit until 6-Jun, 15:00 UT, when its magnification increased at a rate of about 0.08 mag per hour. A peak has been passed near 6-Jun, 22:50 UT. PLANET continues its observations and provides a regularly updated lightcurve showing most recent PLANET and OGLE data.
Modelling of currently available data on OGLE 2004-BLG-273 performed by A. Cassan and D. Kubas shows that the mass ratio between the binary lens components cannot be determined unambiguously, where a model involving a planet appears feasible. Further anomalous behaviour of the lightcurve is expected over the next two weeks involving peaks or even additional caustic passages. Dense photometric observations will resolve the true nature of the lens. This has been reported in PLANET anomaly update 2004 #3-1 (issued 5-Jun, 14:05 UT).
PLANET managed to collect data over the caustic exit in OGLE 2004-BLG-273, which was previously announced in PLANET anomaly alert 2004 #3 (issued 2-Jun, 13:40 UT). The source needed about 15 hours to cross the caustic and finished exiting at 3-Jun 9:40 UT. Most recent data are shown on the regularly updated lightcurve.
A rise in magnification in event OGLE 2004-BLG-273 observed in PLANET data collected with the Danish 1.54m telescope at ESO LaSilla (Chile) led to the prediction that the center of the source star can be expected to exit a fold caustic at 2-Jun, 18:43 UT -2.2 h +3.4 h, which has been reported in PLANET anomaly alert 2004 #3 (issued 2-Jun, 13:40 UT).
First lightcurves containing PLANET 2004 season data have been put on the web.
PLANET has taken first 2004 observing season data with the Danish 1.54m telescope at ESO LaSilla (Chile). Other sites of the network will join in tonight.
The 2004 PLANET season starts on May 1st with Boyden, Perth 0.6m and
On May 31, the Danish 1.54m (ESO), SAAO 1m will be online. We will observe until mid september.
The PLANET team is very pleased to welcome new members, Dave Bennett
(Notre Dame), Stephane Brillant (ESO Paranal), Kem Cook (LLNL/NOAO),
Jadzia Donatowicz (TU Wien), Hannes Calitz, Mattie Hoffman, Pieter
Mentjes, (Boyden observatory), Chris Laws (University of
The new telescope of the network is 1.52m Rockefeller telescope at
The 2003 PLANET season starts on June 1st
ESO 2.2m comes online, and PLANET has round-the-globe coverage for 2002. See here for events currently being observed
The 2002 PLANET season will start on June 1st.
PLANET observations indicate another event, OGLE-2000-BUL-38, is undergoing a rise in magnitude by about 0.15 magnitudes in two days. On 11 July 2000, we issued a electronic alert that the event was rising from the caustic trough and was likely to be undergoing a second caustic crossing soon.
(18-Aug-2000 Update: To see a recent analysis of these data that shows no evidence for a planet orbiting the lens, click here.
PLANET is now monitoring events alerted by the three major microlensing surveys: EROS, MACHO, and OGLE.
In addition, we are readying new special optical-IR cameras to be installed at PLANET observing sites in Chile and South Africa within the next month or two, and a more sensitive optical camera for the PLANET station at Canopus Observatory near Hobart, Tasmania.