As part of the Lick Observatory Supernova Search (LOSS), we have recently identified a highly unusual optical outburst from the nucleus (within 0.05", or 10 pc in projection) of the nearby (d ~ 50 Mpc) spiral (S0/a) galaxy NGC 1589. Over a decade of photometric monitoring with LOSS, together with archival spectroscopy from the CfA Redshift Survey, suggest that the galaxy does not harbor an active nucleus. Likewise, the transient, bright observed X-ray emission and broad H-alpha emission-line profile do not appear to closely resemble those of any known Type II supernova. We therefore consider this transient source (dubbed NGC1589-OT) to be the most viable candidate for a tidal disruption flare (TDF) ever discovered in real time. Here we request UV (STIS) spectroscopy with HST to search for "smoking gun" evidence in favor of the TDF interpretation: photoionized stellar debris ejected by the disruption process. DD time is necessary because the outburst will almost certainly not be visible by the time Cycle 19 observations commence. We did not propose for analogous observations during the normal course of a previous GO cycle due to the extraordinarily small number of good, real-time TDF candidates detected in the past.

We wish to obtain 3 orbits-worth of STIS FUV spectroscopy (G140L grating) of the tidal disruption flare candidate NGC1589-OT. The target acquisition is probably the trickiest part of the observation. We don't have offsets good to < 0.1" from any nearby point sources, so we have to acquire the target directly. Both our optical and (in particular) laser guide star adaptive optics (K-band) imaging suggest the region surrounding the galaxy nucleus (at least within the central 5" relevant for STIS acquisitions) is dominated by the transient point source. We have inputted our observed LGS K-band image into the STIS Target Acquisition Simulator, and find the point source centroiding algorithm works well, so this is what we have chosen. We used a recent observed spectrum of the transient to calculate the appropriate acquisition exposure time. The exposure time calculator suggests we will reach a SNR of 40 with a 0.1 s exposure. We've increased this to 0.5 s for additional signal. The ETC suggests the source would saturate with an exposure time of ~ 15 s, so our flux estimate would need to be off by a factor of 30 for this to be a problem. We note that because we are using the 0.2" slit, we do not need to conduct a peak-up acquisition. Our remaining STIS FUV exposures are configured to maximize exposure time in the remaining orbits. Standard wavelength calibration (performed each orbit) will suffice for our observations. AGN/QUASARS 0 false 0.0 0.0 false false false false SUPPORTED UNIDENTIFIED NUCLEUS UNDESIGNATED V-band magnitude above is integrated over the entire galaxy (several arcminutes in extent). The magnitude of the transient (plus nucleus) is several times fainter. J2000 04 30 45.4500 +00 51 49.16 J2000 STIS/NUV-MAMA Spectroscopic No No G230L 2376 STIS/FUV-MAMA Spectroscopic No No G140L 1425 The scheduling data was generated by CASM 18.3.1. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12437 :visit-id "01" :proposal-version -1 :trans-version "20100902" :date "10-Jan-2011 17:49:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "24" :si-bright-earth-limb-angle 20.0 :data-volume 278864 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12437 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12437 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2901 :al-overhead-at-end 200 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12437 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 200 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12437 :visit-id "01" :orbit-number 3 :pcs-time 222 :si-vis-utilization 3012 :al-overhead-at-end 200 :internal-dur-at-end 321 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3234 :pcs-gap 0 ) true 3 0