This is the revised version of GO-11716. The former ACS/HRC observations have been changed to WFC3/UVIS ----- Attempting Submission 1 (Sat Jul 19 22:29:44 GMT 2008) ----- ----- Attempting Submission 2 (Wed Jul 01 00:17:02 GMT 2009) ----- Assigned ID: 238 ----- Attempting Submission 1 (Fri Mar 07 00:48:13 GMT 2008) ----- M31 RV is a luminous red variable star that appeared in the bulge of M31 in 1988. During its outburst, which lasted a few months, it was one of the brightest stars in the Local Group. Unlike a classical nova, it was extremely cool during the eruption, and it never became optically thin or exposed a hot, blue source. There has been renewed interest in M31 RV recently, because of its remarkable similarities to V838 Mon, a luminous Galactic variable star that underwent a similar rapid expansion to become a red supergiant, and which is currently illuminating a spectacular light echo, extensively observed by HST. The outburst mechanism for this new class of luminous transients remains unknown, and is one of the major current challenges to our understanding of stellar physics. Bond and Siegel have examined WFPC2 frames of the site of M31 RV, obtained fortuitously in 1999 as parallel observations during spectroscopic studies of the nucleus of M31. The explosion site shows only a pure old population of red giants, with no obvious remnant of M31 RV. I propose now to obtain second-epoch images of the site, in the same filters, to determine whether there is an object in the field that has faded or varied, and if so what its brightness and color is. This information may provide new constraints on proposed outburst mechanisms, such as stellar mergers or collisions, and could lead to a spectroscopic observation in a future HST cycle.

Previous description: I will obtain ACS/HRC images of the site of M31 RV in F555W and F814W. A three-point dither pattern will be used, with exposures of 450 sec in V and 300 sec in I at each of the 3 points. June 2009 revision: Since ACS/HRC was not repaired in AM4, I am changing to WFC3/UVIS. A three-point dither will be used, with exposures of 565 sec in V and 325 sec in I at each of the 3 points. I am greatly increasing the total exposure time possible during the single orbit by using the UVIS1-M512-SUB subarray. COOL STARS 12 false 0.0 0.0 false false false false false SUPPORTED EXT-STAR BULGE M III-I J2000 00 43 2.3000 +41 12 56.00 J2000 ACS/HRC Imaging No No F555W ACS/HRC Imaging No No F814W The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /var/tmp/OPVisit14981.xml 1246407251851 (Tic-Visit :proposal-id 11716 :visit-id "01" :proposal-version -1 :trans-version "20090130" :date "30-Jun-2009 20:14:05.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 26224 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11716 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11716 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3014 :al-overhead-at-end 42 :internal-dur-at-end 67 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3351 :pcs-gap 0 ) true 1 0