6475( 6) - 02/13/96 16:10 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6475 Version: 6 Check-in Date: 13-Feb-1996 16:01:26 1.Proposal Title: High Resolution Imaging of Unstable Massive Stars at the Top of the HR Diagram ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle HOT STARS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Roberta Humphreys University of Minnesota CoI: Kris Davidson University of Minnesota Y CoI: Terry Jones University of Minnesota N CoI: Robert Gehrz University of Minnesota N CoI: Joachim Krautter Landessternwarte,Heidelberg N ------------------------------------------------------------------------------------ 6. Abstract A few highly unstable, very massive stars lie on or near the empirical upper luminosity boundary in the HR diagram. These include the Luminous Blue Variables, the cool hypergiants and other even rarer objects, all related by the violent mass- loss phenomena responsible for the upper boundary. We propose to obtain high-spatial resolution WFPC2/BV images of IRC+10420 a cool hypergiant and OH/IR star with visible nebulosity. Our groundbased optical nad infrared observations, including polarimetry and spectroscopy, revealed a rich and complex circumstellar environment with an equatorial disk surrounded by diffuse and clumpy gas and dust. Recent 10micron imaging shows an extended bipolar structure. The HST images are needed for studies of the morphology of the ejecta and for comparison with our infrared and radio observations. ------------------------------------------------------------------------------------ 6475( 6) - 02/13/96 16:10 - [ 2] Observations Description ------------------------ Reasons for the observing plan are described here, as well as the plan itself. ----- (1. GENERAL INFORMATION:) IRC+10420 is a bright hypergiant star with detectable ejecta and nebulosity. In our ground-based optical and near-IR images the object is extended 1--2 arcsec in the N-S direction, and a recent 10 -micron image shows probable bipolar structure as much as 8 arcsec across. At a distance of 5 kpc for IRC+10420, the PC resolution of about 0.001 pc will allow us to resolve the complex structures that we have good reason to believe are present. At WFPC2 wavelengths we expect this to be mainly reflection nebulosity plus perhaps some emission lines; there is a limited analogy with the Homunculus nebula of Eta Car, ----- (2. BASIC PLAN:) A large dynamic range is needed, because the central star is bright while the outlying nebulosity may be quite faint. We plan to obtain this by using a wide range of WFPC2 integration times. The shortest exposure times will be short enough to image the star without data-saturation; the longest will be determined by the amount of time available; and intermediate exposure times will also be used in order to obtain maximum S/N for intermediate brightness levels. More than one filter is needed, in order to get color information. Of course we use the PC quadrant of the WFPC2. ----- (3. CHOICE OF FILTERS:) IRC+10420 is very red (B-V ~ 2.7 magn) because of interstellar reddening. Therefore we choose filters in the B-to-V wavelength range. Violet filters would require long exposure times. Red filters are inappropriate because the (nebulosity/star) brightness ratio is small for reflection nebulosity at red wavelengths, and because the star is awkwardly bright at such wavelengths. We do NOT use wide filters such as F439W, F555W, and F569W, because their effective wavelengths would be uncertain and position- dependent for such a reddened object, and because we want to minimize emission- line contributions so that we're sure of what we're looking at. Therefore we choose to use filters F467M (pseudo-B) and F547M (V). Assuming magnitudes B = 13.7 and V = 11.0, the central star will produce roughly 4000 and 110000 counts per second with F467M and F547M respectively (i.e., CCD electrons per second in the entire star image). ----- (4. IMAGING WITH F467M:) First we do a single 12- second exposure to get the star itself without any data-saturation. Then, two 30-second exposures at slightly different positions (what STScI calls "dithering") in order to image bright stuff close to the star. The two different positions are chosen to get maximum possible effective resolution, i.e., they are separated by half-integer numbers of pixels to make the sampling very good. These two different positions will also be helpful for patching over instrument defects. Then, two long exposures, each at least 140 seconds, to detect fainter outlying material. These are taken at slightly different positions ("dithering" again, if one insists on calling it that), separated by integer numbers of pixels this time, to help patch over CR hits and instrument defects. ----- (5. IMAGING WITH F547M:) Our data with this filter can be used in combination with the F467M data to make a color map, but the observing plan is optimized differently. We don't have enough time to "dither" the F547M observations. F547M will be more useful for detecting the faintest outlying stuff (because the interstellar reddening is high), but F467M is better adapted to small-scale details (because this is a reflection nebula). The range in exposure times is much larger for F547M: An exposure time of less than a second is needed to image the star itself without data saturation, while we use an integration time longer than 100 seconds for the deepest exposure. Intermediate exposure times are used so that every intermediate brightness level has an exposure that gives excellent S/N. Note that our longest specified F547M exposure time, 2 140-second integrations, should be increased if time available in the orbit permits it. Real Time Justification ----------------------- None, but note the following---- R. D. Gehrz and J. Krautter have initiated a series of supporting IR imaging studies of IRC +10420 and VY CMa at ESO using the IRAC-2 near-IR camera on the 2.3-meter and the TIMMI mid-IR camera on the 3.6-meter. The first images of IRC +10420 at 2.3 and 10 microns were recorded in May, 1995, and have been analyzed, showing evidence for a bipolar dust nebula. Additional observations are scheduled for April and May 1996. Since this is a variable target object, it is highly desirable not to delay the HST observations more than necessary after that time. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 6475( 6) - 02/13/96 16:10 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address*Prof. R.M. Humphreys*Astronomy Dept.*116 Church St. SE*Minneapolis, MN 55455 Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 6475( 6) - 02/13/96 16:10 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 100 IRC+10420 STAR, F0-F2, LUMINOUS RA=19H 26M 48.09S +/- 0.1S, 2000 V = 11.0+/-0.5 BLUE VARIABLE, DEC=+11D 21' 17.7" +/- 1.5", B-V = 2.7+/-0.5 IRREGULAR VARIABLE PLATE-ID=02V0 E(B-V) = 2.5+/-0.7 Comments: Brightness of the ejecta/halo is not known but probably spans a large range of surface brightness, in radius several arcsec. 6475( 6) - 02/13/96 16:10 - [ 5] Visit: 01 Visit Requirements: BETWEEN 01-APR-96 AND 05-MAY-96 On Hold Comments: Additional Comments: Large dynamic range obtained by exposures with wide range of integration time. IMPORTANT: We had difficulty filling the complete orbit, merely because of peculiarities in RPS2. We'd like to increase the longest exposure times (exposure numbers 130 and 250) to the maximum values possible. Exposures 110, 120, 210, and 220 should NOT be increased. Reasoning behind the plan is outlined in the Observing Description section. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 110 IRC+10420 WFPC2 IMAGE PC1 F467M 1 12S SEQ 110-130 NON-INT;MAX DUR Comments: Short exposure to get peak of central star without data saturation. ------------------------------------------------------------------------------------------------------------------------------------ 120 IRC+10420 WFPC2 IMAGE PC1 F467M DITHER- 1 30S TYPE=LINE,DITHE R-LINE- SPACING=0.161 Comments: Half-integer dither spacing (2.5,2.5) pixels, for best sampling; closer spacing than the default value. The exposure time should not be increased; we would have used a MAX DUR special requirement but RPS2 protested. ------------------------------------------------------------------------------------------------------------------------------------ 130 IRC+10420 WFPC2 IMAGE PC1 F467M DITHER- 1 140S TYPE=LINE,DITHE R-LINE- SPACING=0.322 Comments: Integer dither spacing (5,5) PC pixels, different from exposure 120. This integration time should be lengthened if possible, see Visit Comments ------------------------------------------------------------------------------------------------------------------------------------ 210 IRC+10420 WFPC2 IMAGE PC1 F547M 1 0.5S SEQ 210-250 NON-INT; MAX DUR Comments: Short exposure to get peak of central star without data saturation ------------------------------------------------------------------------------------------------------------------------------------ 220 IRC+10420 WFPC2 IMAGE PC1 F547M 1 3S MAX DUR ------------------------------------------------------------------------------------------------------------------------------------ 230 IRC+10420 WFPC2 IMAGE PC1 F547M 1 10S MAX DUR 12S ------------------------------------------------------------------------------------------------------------------------------------ 240 IRC+10420 WFPC2 IMAGE PC1 F547M 1 40S MAX DUR 45S ------------------------------------------------------------------------------------------------------------------------------------ 250 IRC+10420 WFPC2 IMAGE PC1 F547M 2 150S Comments: This integration time should be increased if possible, see Visit Comments. Integration time should be nearly the same for both of the 2 integrations. ------------------------------------------------------------------------------------------------------------------------------------ 6475( 6) - 02/13/96 16:10 - [ 6] Summary Form for Proposal 6475 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters DITHER-TYPE=LINE DITHER-LINE-SPACING=0.161 DITHER-LINE-SPACING=0.322 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category HOT STARS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BETWEEN 01-APR-96 AND 05-MAY-96 SEQ 110-130 NON-INT;MAX DUR SEQ 210-250 NON-INT; MAX DUR MAX DUR 12S MAX DUR 45S ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F467M F547M ------------------------------------------------------------------------------------------------------------------------------------ Target Names IRC+10420 ------------------------------------------------------------------------------------------------------------------------------------