The currently accepted theory regarding the last stages of massive star evolution maintains that the evolution of the envelope is coupled to that of the stellar core. For this reason, very massive stars are expected to shed their outer hydrogen envelopes before they develop large iron cores, and ultimately, explode as core-collapse supernovae (SNe). It is therefore a strict prediction of current models that massive stars (certainly those above ~40 solar mass) will explode as hydrogen-poor SNe, i.e., of Types Ib and Ic. In particular, the class of luminous blue variables (LBVs) such as eta-Carina, which are known to be very massive (up to 100 solar masses and above) are expected to lose their entire hydrogen envelopes prior to their ultimate explosions as SNe. However, using pre-explosion HST/WFPC2 imaging of the location of the recent hydrogen-rich type IIn SN 2005gl, we have identified (Gal-Yam et al. 2007) its putative progenitor as a very luminous point source (with absolute V magnitude of -10.2). If this is a single star, it must be an LBV from luminosity considerations (no other stars are as luminous). If our progenitor identification is correct, at least in some cases, massive stars explode before losing most of their hydrogen envelope, indicating the core and envelope are decoupled, and requiring revision of stellar evolution theory. Here, we propose a single-orbit HST observation of the location of SN 2005gl designed to test whether the point source we identified as its LBV progenitor has indeed disappeared (as expected from a single star) or remained unchanged (as expected, e.g., if it is a compact star cluster). These data are the last observational ingredient required to firmly establish (or refute) the explosion of an LBV as a type IIn SN, with fundamental implications for the theory of massive star evolution. Since the new data will be compared to pre-explosion WFPC2 images, this program is perfectly suited to be carried out with the WFPC2 camera.

We will observe the location of SN 2005gl using the F547M filter for one orbit, to determine whether the putative progenitor star of the SN has indeed disappeared. RESOLVED STELLAR POPULATIONS 12 false 0.0 false false false false false false SUPPORTED STAR ETA CARINAE STAR LUMINOUS BLUE VARIABLE SUPERNOVA TYPE II J2000 00 49 50.0000 +32 16 57.00 J2000 WFPC2 Imaging No F547M Single visit in this proposal (Tic-Visit :proposal-id 11105 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "11-May-2007 10:30:22.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11105 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11105 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3152 :pcs-gap 0 ) true 1 0 Single visit in this proposal This is a repeat of visit 1 (Tic-Visit :proposal-id 11105 :visit-id "01" :proposal-version -1 :trans-version "20070325" :date "11-May-2007 10:30:22.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "26" :si-bright-earth-limb-angle 20.0 :data-volume 179264 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11105 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11105 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2700 :al-overhead-at-end 180 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3152 :pcs-gap 0 ) false 1 0