----- Submission 1 (Tue May 16 20:54:29 GMT 2006) ----- Assigned ID: 333 ----- Submission 1 (Fri Jan 27 19:04:21 GMT 2006) ----- A SNAP Image of the Circumstellar Ejecta of AE And in M31 The "supernova impostor" or Luminous Blue Variable AE Andromedae in M31 has a spectrum that more closely resembles eta Car than any other known LBV, including the presence of anomalously strong and peculiar Fe II emission. An early FOC ultraviolet image of AE And showed a faint, fuzzy extension of the presumed stellar object. This may be nebulosity from an earlier eruption, or a very nearby UV-bright star. Possibly AE And is embedded in a bipolar nebula. In any case, 2-color ACS/HRC imaging will show the nature of this object. The presence of ejecta will be relevant to understanding the anomalous emission. If nebulous, the shape and extent of the ejecta can provide information on the wind geometry. An extended bipolar structure, similar to eta Car, would be especially interesting as it may be a clue to the mechanism of the more energetic giant eruptions.
One orbit is sufficient. Will image AE Andromedae with ACS/HRC, using filters F435W, F555W, and F625W. (Re. filters, see "additional comments.") Since the object is faint, long exposures are not expected to cause saturation. Since high spatial resolution is highly desirable, will box-dither the F435W exposures to improve spatial sampling. For the other filters, simple 2-point dither should be adequate for bad-pixel removal. -- -- no scheduling constraints are requested -- -- none requested -- The original proposal named only two filters, F435W and F625W. Now we find, however, that there is sufficient visibility time to include a third, F555W. This is useful in the following way. Small-scale diffuse material around AE Andromedae may be either a reflection nebula or a photoionized nebula. In the latter case, bright H-alpha emission would contribute to an F625W exposure but not F555W. Therefore we hope that 3 filters will show the difference between a reflection nebula and an HII region. -- There is no serious scientific disadvantage to using the third filter, since F555W + F625W together will achieve the goals originally intended for F625W alone in any case. There is a resulting decrease in the total amount of integration time, but not to a serious extent. The third filter doesn't conflict with any other users' plans, since no one else intends to observe this object. --- HST's spatial resolution is better with the F435W filter. Therefore a 4-point box dither pattern is used for it (partly to improve the sampling), but a simpler line pattern is OK for F555W and F625W. Bad-pixel removal will probably be simple because the target object is expected to be quite small, most likely less than 30 x 30 ACS/HRC pixels. ISM AND CIRCUMSTELLAR MATTER 12 false 0.0 false false false false false SUPPORTED EXT-STAR CIRCUMSTELLAR MATTER EJECTA EMISSION LINE STAR ETA CARINAE STAR LUMINOUS BLUE VARIABLE Located in M31. Position listed here was estimated using APT/VTT. J2000 00 43 2.0000 +41 49 12.00 J2000 ACS/HRC Imaging No No F435W ACS/HRC Imaging No No F625W POS-TARG DITHER 0.15 Dither is intended partly to improve sampling with shortest-wavelength filter used here, F435W. Target is small, less than 2 arcsec diameter and probably less than 1 arcsec. -- This is the default dither box given by APT. Can its parameters be improved? LINE 0.098 false false 63.5 4 19.89 ACS-HRC-DITHER-BOX 1 false POS-TARG DITHER 0.198 Simple 2-point pattern suffices for F555W and F625W, for two reasons: (1) At these wavelengths there is no great need to improve the ACS/HRC sampling size. (2) Since the target object is expected to be small, maybe about 30 x 30 HRC pixels, there will probably be only a few relevant bad pixels. LINE false false 2 44.28 ACS-HRC-DITHER-LINE 2 false /eadata/kd/HSTcy15ph2/OP-cache/10796aea_ph2-v01.xml (Tic-Visit :proposal-id 10796 :visit-id "01" :proposal-version -1 :trans-version "20060322" :date "16-May-2006 15:28:33.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 147216 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 10796 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 10796 :visit-id "01" :orbit-number 1 :pcs-time 355 :si-vis-utilization 2814 :al-overhead-at-end 0 :internal-dur-at-end 199 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3169 :pcs-gap 0 ) true 1 0 /eadata/kd/HSTcy15ph2/OP-cache/10796aea02-v01.xml Reason for POS TARG: This is an extra precaution for the bad-pixel removal process. If an especially bad pixel falls on the rather small target object for the F625W exposures, then the relatively large POS TARG specified here will ensure that the F555W and F625W exposures will not be affected by the same bad pixel. The specified POST TARG is intended to be dX = -30 HRC columns, dY = -30 rows; but the precise size of this offset is not critical. Re. POS TARG, see comments for F625W exposure in same pattern.