5986( 4) - 12/01/95 15:13 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 5986 Version: 4 Check-in Date: ********** 1.Proposal Title: B, V, H Alpha and UV Imaging of the Central 1 kpc of M81 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle Galaxies & Clusters GO 5 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: Nick Devereux New Mexico State University CoI: Holland Ford Johns Hopkins University,Dept. of Physics N & Astronomy,Baltimore, MD 21218 CoI: George Jacoby Kitt Peak National Observatory,PO Box N 26732,Tucson,AZ 85726 ------------------------------------------------------------------------------------ 6. Abstract M81 is a nearby (3.6 Mpc), early-type (Sab) spiral galaxy that hosts a weak Seyfert 1 nucleus embedded in a bright nuclear spiral of H Alpha emission. The nuclear spiral is remarkably similar to that discovered in the nucleus of M31 by Jacoby et. al. (1985, ApJ 290, 136). Narrow band H Alpha imaging with WFPC2 will reveal the spatial distribution of the ionized gas within the central 1.36 kpc diameter region of M81 at 0.2'' resolution. UV imaging with WFPC2 will reveal the distribution of hot ionizing stars at the same resolution. The UV image will help determine whether or not the nuclear H Alpha spiral is photoionized by hot stars. Finally B and V band imaging with the FOC will help elucidate whether or not M81 has multiple nuclei like its nearer counterpart M31 (Lauer et. al. 1993, AJ 106, 1436). ------------------------------------------------------------------------------------ 5986( 4) - 12/01/95 15:13 - [ 2] Observations Description ------------------------ centerline H Alpha Imaging with WFPC2 An H Alpha image of the center of M81 was obtained by Ford et. al. using the PC array of WFPC1 in Cycle 3, but the resulting images were disappointing due to the fact that they were compromised by two serious problems associated with HST. First, the resolution of the images was significantly degraded by the spherical aberration caused by the incorrectly figured primary mirror. The second problem is related to the filter used for the observations. The rest wavelength H Alpha filter F656N was thought to have delaminated forcing Ford et. al. to use the less suitable redshifted H Alpha filter F664N. With a velocity of -43 kms, M81 is actually blueshifted, not redshifted. Consequently, the H Alpha line fell at about the 50\ point in the redshifted H Alpha filter causing considerable loss of signal. Given these two problems it is perhaps not surprising that the existing HST H Alpha image of M81 does not show the filamentary emission revealed in the ground based H Alpha image (see attached figure). There is clearly a need to repeat the HST observation now that a proper H Alpha filter can be used and the spherical aberration is corrected. We are proposing to use WFPC2 to obtain an H Alpha line + continuum image of M81 using the F656N filter and a continuum only image using the F588N filter. The nucleus of M81 will be centered on a WF array rather than the PC array. The WF has twice the FOV of the PC array and the S/N is approximately doubled for the same integration time. The WF array is the best given the extent of the filamentary H Alpha emission and the requirement for high sensitivity. The alignment of the other WFPC2 arrays is not important for this observation. The success of our proposal depends on detecting H Alpha above the shot noise in the continuum. We used the H Alpha and continuum brightnesses measured from unpublished ground based images and the information provided in the WFPC2 instrument handbook to estimate a total integration time of 50 minutes through the F656N H Alpha filter. Ideally, we would like to use the F547M filter to measure the continuum emission, but unfortunately we expect the bright V = 15 mag/arcsec^2 nucleus of M81 to saturate the WF array in about 30 seconds Consequently, we will measure the continuum emission with the much narrower F588N filter. The F588N filter includes the Na D absorption line but since the absorption feature is stellar in origin we expect it to track the stellar continuum to first order. The exposure time for the F588N off-band filter is 32 minutes. Both the line and continuum exposures will have to be divided into shorter 10 and 4 minute exposures respectively to avoid saturating the bright nucleus. The total exposure time is 50 min F656N, 13 min (overhead) and 32 min (F588N), 20 min (overhead). \medskip centerlinebfUV Imaging with WFPC2 We are also proposing to use the F160BW woods filter in WFPC2 to obtain a UV (1590 Angstrom) image of the same field imaged in H Alpha. The UV image will allow us to identify the location and brightness of any hot stars that may be responsible for ionizing the nuclear H Alpha spiral clearly visible in ground based H Alpha images (see attached figure). We have selected the WFPC2 camera over the FOC for 2 reasons. First, the UV filters in the FOC suffer from significant red light leaks which complicated interpretation of the UV images obtained for the center of M31 by King et. al. (1992, ApJ 397, L35). Second, since we plan to compare the UV image directly with the H Alpha image, it makes sense to use the same camera as will be used for the H Alpha image. Consequently, we will use the F160BN15 filter in conjunction with WF3. Following the prescription in the WFPC2 instrument handbook, we estimate that a total integration time of 40 minutes will be sufficient to reveal individual BO stars, which will have V magnitudes = 24 at the distance of M81, with a S/N ~ 5. we propose 2 * 20 minutes through the F160BW filter with 5 minutes of overhead. \medskip centerline High Angular Resolution B and V band Imaging with the FOC We are also proposing to use the highest angular resolution, 0.04'', imaging capability of the FOC at F/96 to search for multiple nuclei in the central 7'' * 14'' region of M81. The FOC has the capability to resolve individual sources in M81 that are as close as 0.7pc. The FOC will be centered on the nucleus of M81 and exposed for an integration time of 40 minutes in the B band (F430W) and the V band (F480LP). The optical continuum emission of the nucleus is dominated by starlight (Peimbert & Peimbert 1981, ApJ 245, 845; Filippenko & Sargent 1988, ApJ 324, 134). The size of the broad line region associated with the Seyfert 1 nucleus is estimated to be 1 x 10 ^ -4 arc sec (Filippenko & Sargent 1988, ApJ 324, 134) which is far too small to be resolved by HST. Radio interferometry places an upper limit of 4 x 10 ^ -4 arc sec on the source size at 5 GHz (Kellerman et. al. 1976, ApJ 210, L121). Consequently, the imaging we are proposing is unlikely to yield anything new about the nature of the Seyfert nucleus, but we will be able to search for multiple nuclei. Imaging through both the B and V filters will allow the B-V color to be measured in the central 7 x 14 arc sec region of M81 which will provide some capability with which to assess the impact of dust obscuration on the B and V band morphology. If the bright, V= 15 mag/arc sec^2, nucleus of M81 remains unresolved with the FOC then, using the information provided in the FOC instrument handbook we estimate the count rate in the central pixel to be 37 counts/sec which is greater than the 1 counts/sec rate above which the detector becomes non-linear. Consequently, it will be necessary to use a neutral density filter (F4ND) to cut the count rate down to unity. If the nucleus is unresolved by the FOC then we can expect a signal to noise ratio of ~ 500 in a total integration time of 10 minutes. If there is a second nucleus near the bright unresolved AGN, it will be fainter and require a long integration. Consequently, we propose to take a long exposure (40 minutes) through each of the F430W and F480LP filters. \medskip centerline Observation Summary M81, by virtue of its high declination (69 ^ o), is a continuous viewing zone target which means that HST can point at it for entire 96 minute orbits without being occulted by the Earth. The schematic time line will be WFPC2: 12 min (Acq), 5 * 10 min F656N, 13 min (overhead), 8 * 4 min F588N, 20 min (overhead), 2 * 20 min F160BW, 5 min (overhead); FOC: 12 min (Acq), 40 min F430W, 7 min (overhead), 40 min F480LP, 7 min (overhead). The total time is 278 min, which is 3 CVZ orbits. Real Time Justification ----------------------- none none Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 5986( 4) - 12/01/95 15:13 - [ 3] Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: UPS Email: , ------------------------------------------------------------------------------------ 5986( 4) - 12/01/95 15:13 - [ 4] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3031 Galaxy,Spiral RA=9H 51M 27.34S +/- 0.03S, 1950 V = -43 SURF(V) = 15.3 DEC=69D 18' 8.2" +/- 0.2" 5986( 4) - 12/01/95 15:13 - [ 5] Visit: 01 Visit Requirements: ORIENTation 225D TO 270D CVZ On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC3031 WFPC2 IMAGE WF3-FIX F656N 6562 ATD-GAIN=7, CR- 1 600S POSition TARGet 9.0,18.0 SPLIT=NO Comments: gain 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC3031 WFPC2 IMAGE WF3-FIX F547M 5454 ATD-GAIN=7 1 30S SAME POSition AS 1 Comments: 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC3031 WFPC2 IMAGE WF3-FIX F160BN15 1471 ATD-GAIN=7, CR- 1 1000S SAME POSition AS 1 SPLIT=NO Comments: gain 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC3031 WFPC2 IMAGE WF3-FIX F656N 6562 ATD-GAIN=7, CR- 1 600S POSition TARGet 9.425,17.575 SPLIT=NO Comments: gain 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC3031 WFPC2 IMAGE WF3-FIX F547M 5454 ATD-GAIN=7 1 30S SAME POSition AS 4 Comments: gain 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC3031 WFPC2 IMAGE WF3-FIX F160BN15 1471 ATD-GAIN=7, CR- 1 1000S SAME POSition AS 4 SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC3031 WFPC2 IMAGE WF3-FIX F656N 6562 CR-SPLIT=NO, 1 600S POS TARG 8.575,18.425 ATD-GAIN=7 Comments: gain 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC3031 WFPC2 IMAGE WF3-FIX F547M 5454 ATD-GAIN=7 1 30S SAME POSition AS 7 Comments: gain 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC3031 WFPC2 IMAGE WF3-FIX F160BN15 1471 ATD-GAIN=7, CR- 1 1000S SAME POSition AS 7 SPLIT=NO Comments: gain 7e/DN ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC3031 FOC/96 IMAGE 512x512 F480LP, 5100 PIXEL=25x25 1 3000S F4ND Comments: consecutive with WFPC2 exposures ------------------------------------------------------------------------------------------------------------------------------------ 5986( 4) - 12/01/95 15:13 - [ 6] Summary Form for Proposal 5986 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 FOC/96 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ATD-GAIN=7 CR-SPLIT=NO PIXEL=25x25 ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category Galaxies & Clusters ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENTation 225D TO 270D CVZ POSition TARGet 9.0,18.0 SAME POSition AS 1 POSition TARGet 9.425,17.575 SAME POSition AS 4 POS TARG 8.575,18.425 SAME POSition AS 7 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F656N F547M F160BN15 F480LP, F4ND ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC3031 ------------------------------------------------------------------------------------------------------------------------------------