Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 4635c Report Date: 09-May-96:19:45 Version: ********** Check-in Date: ********** 1.Proposal Title: TESTING THE ACCRETION DISK LINE-PROFILE HYPOTHESIS IN ARP 102B: CYCLE3MEDIUM ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID QUASARS & AGN GO Sub Category RADIO GALAXIES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Prof. Alexei V. Filippenko UC-BERKELEY USA ------------------------------------------------------------------------------------ 7. Abstract Arp 102B is the prototype of a set of ten broad-line radio galaxies whose hydrogen Balmer line profiles are double-peaked, and which share several additional distinguishing optical characteristics. We have recently established the reality of this class through a comprehensive optical spectroscopic survey of radio-loud AGNs at z < 0.4 (Eracleous and Halpern 1992a,b). We now propose to obtain moderate- resolution spectra to study the UV emission lines and nonstellar continuum of Arp 102B. Several theories have been suggested to explain the unusual line profiles; the most specific is a model for emission from the photoionized atmosphere of an accretion disk. The Balmer lines are the only broad lines detected in ground-based spectra, and the optical nucleus is dominated by starlight. Both of these limitations restrict further progress in understanding the nature of this peculiar spectrum. But observations of the UV emission lines and continuum could test this model by (1) measuring line profiles of species with different ionization potentials, and (2) measuring the nonstellar continuum, which should be different from that of most AGNs. Disk photoionization models predict line shapes which are different among the UV lines. The ionizing continuum is predicted to be nonthermal, arising in an optically thin, ion-supported torus, rather than a blackbody accretion disk. If supported by the results of HST spectra, our study of Arp 102B could provide the most direct view of an accretion disk in an AGN. ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 7.47 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: FOS ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 4635c PI: Prof. Alexei V. Filippenko Proposal Title: TESTING THE ACCRETION DISK LINE-PROFILE HYPOTHESIS IN ARP 102B: CYCLE3MEDIUM ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Pi Alexei V. Filippenko UC-BERKELEY USA Jules P. Halpern COLUMBIA UNIVERSITY USA Kaiyou Chen LOS ALAMOS NATIONAL LAB USA Michael C. Eracleous COLUMBIA UNIVERSITY USA ------------------------------------------------------------------------------------ 3. Description of proposed observations. To detect faint lines, to model in detail the profiles of broad lines, and to determine the overall shape of the continuum, we require spectra having good S/N ratio and modest resolution over the entire accessible UV wavelength range. We will connect the red end of the UV spectrum (around 3150 A) with our optical spectra, obtained at ground-based observatories. This will give a reliable continuum shape over the range 1150-10000 A, and it will allow us to obtain accurate emission-line intensity ratios between UV and optical lines. Three HST grating settings are needed, as follows: (1) FOS, G130H grating, 1150-1608 A, 1.0 A/diode, blue digicon. (2) FOS, G190H grating, 1573-2323 A, 1.5 A/diode, red digicon. (3) FOS, G270H grating, 2227-3306 A, 2.1 A/diode, red digicon. The FOS spectra will be obtained through the 4.3" X 4.3" aperture (effectively 4.3" X 1.4", due to diode size). This yields the best throughput, and the resulting resolution will be adequate for our purposes. At UV wavelengths, the starlight contamination through this aperture will be small compared with light from the active nucleus. Thus, the spherical aberration of HST does not affect us very much (except for the broad wings on the line profile). The first setting above gives us Ly-alpha and C IV 1549, two very important lines. Most of the Ly-alpha profile will be redshifted away from the geocoronal emission. The second setting includes He II 1640 and C III] 1909, while the most important lines in the third setting are C II] 2326, [Ne IV] 2423, and Mg II 2800. We might also detect Fe II blends. Together, these grating settings will allow us to determine whether there is a UV bump in the continuum. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. Until now, the hydrogen lines are the only broad lines which have been seen in Arp 102B. IUE observations of Arp 102B have resulted in weak detections of continuum and Ly-alpha. SWP and LWP exposures of duration 265 and 120 minutes, respectively, barely detected continuum in the 1600-3000 A range (Chen et al. 1989), consistent with an extrapolation of the optical continuum. The only UV emission line detected by IUE was Ly-alpha, but the resolution and S/N ratio are low. Its velocity width appears to be much less than that of the Balmer lines, a very suggestive result. On the other hand, at least half of the Ly-alpha flux could be coming from the narrow-line region, which would be consistent with typical narrow-line ratios. We must obtain a much better profile and a more accurate measurement the continuum shape if meaningful conclusions about the origin of the emission lines are to be drawn. Other, weaker UV lines must also be studied. HST is the only telescope that can provide the necessary data on the emission lines and nonstellar continuum. These data will test the theory of the origin of emission lines in a photoionized disk atmosphere. If the theory survives the observations, physical properties such as ionization parameter and density in the photoionized disk atmosphere could be estimated for the first time in an AGN accretion disk. An important supporting piece of data that will aid in the interpretation of the ionizing continuum is the soft X-ray spectrum. X-ray observations of Arp 102B have already been obtained with the ROSAT PSPC, and will be available for archival analysis by the time the HST observations are made. From the IUE data of Chen et al. (1989), we estimate that the observed continuum flux density of Arp 102B at 1400 A, 1700 A, and 2300 A is 0.05 mJy, 0.10 mJy, and 0.18 mJy, respectively. FOS, G130H grating, blue digicon: At 1400 A, the efficiency is 0.007. The throughput of the 4.3" X 4.3" aperture is 0.47 for point sources, and we have 1.0 A/diode. Using equation (5) of Table 1.2.1 in the FOS Instrument Handbook, we find a count rate of 0.008 per second per diode. Zodiacal light, airglow, and diffuse Galactic light will not significantly affect our observations. The dark current is comparable to the expected signal; thus, the exposure time must be doubled to achieve the desired S/N ratio, compared with the case of negligible dark current. Rebinning the data to 2 A/bin, we therefore require 242 minutes for S/N = 11 in the continuum at 1400 A. FOS, G190H grating, red digicon: At 1700 A, the efficiency is 0.02. The throughput of the 4.3" X 4.3" aperture is 0.52, and we have 1.47 A/diode. The derived count rate is 0.06 per second per diode in the continuum. Background sky and dark current are negligible; thus, the integration time is equal to (S/N)**2/count-rate. For S/N = 23, we require 143 minutes. FOS, G270H grating, red digicon: At 2300 A, the efficiency is 0.06. The point-source throughput is 0.55, and there are 2.09 A/diode. The derived continuum count rate is 0.37 per second per diode. Sky and dark current are entirely negligible. For S/N = 36, we require 60 minutes. Please add 18M to G130H (total = 260M) and 3M to G190H (total = 146M) if the extra time needed for ACQ/PEAK is not charged to the GO (see Question 5). Page 4 ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. Originally I had assumed that ACQ/BINARY would be used to acquire the target. However, during a visit to STScI I was told this would be quite risky for a galaxy, even though it has a star-like nucleus (it is an active galaxy). The reason is that the background is uneven, and also the apparent brightness depends on how much of the "fuzz" is integrated. Moreover, the nucleus itself might even be resolved on the 0.3" scale. So, I reluctantly decided to play it safe and use ACQ/PEAK instead. Since the total spacecraft time exceeds 6 hours, the peak-up has to be done for the blue and red sides separately (i.e., side-switching is not allowed). I have put relatively long integration times for the dwells, in order to be certain of getting enough counts for successful acquisition. The first spatial scan will be 3 X 1 with the 4.3" aperture; each dwell should be 1 s on the red side, and 8 s on the blue side. The second spatial scan will be 2 X 6 with the 1" circular aperture; each dwell should be 2 s on the red side, and 12 s on the blue side. (The object is quite red.) The science observations will be conducted with the 4.3" aperture. If it turns out that the extra time for peak-up acquisitions is NOT charged to the GO, please ADD 18M (total = 260M) to the FOS/BL G130H science integration (exposure line 7), and ADD 3M (total = 146M) to the FOS/RD G190H integration (exposure line 4). This will make the total time equal to the allocated spacecraft time, if ACQ/BINARY had been used. Thank you. ------------------------------------------------------------------------------------ 6. Description of special calibration exposures. None. ------------------------------------------------------------------------------------ 7. Data reduction and analysis plans. Measurement and analysis of the calibrated one-dimensional spectra will be done with an extensive program written by the PI for his studies of optical spectra. All emission lines will be measured (wavelengths, fluxes, equivalent widths, velocity widths), and the continuum shape will be determined. We will fit accretion disk line profiles to each broad emission line; the variation of line emissivity with radius will be parametrized as a power-law index. Alternatively, direct deconvolution techniques can be used to derive the emissivity as a function of radius, without reference to an analytic form Direct comparison with detailed photoionization predictions for the line profiles can also be made. Comparisons of the derived radii for different lines can be used to search for stratification into zones of different ionization potential. The fit to the power -law emissivity index will yield information about the geometry and extent of the ionizing source. The UV-optical nonstellar continuum of Arp 102B will be compared with that of other AGNs to look for similarities (e.g., UV bump and/or power law) and differences. Perhaps a new type of spectrum, possibly attributable to the hypothesized ion torus, will be found. There will also be information about the soft X-ray/EUV spectrum from archival ROSAT observations that have already been obtained, so that a better description of the ionizing continuum can be made. These data will be used in a more accurate analysis of the energy budget of the photoionized disk atmosphere. A true photoionization model which incorporates the geometries of the disk and ionizing source will be attempted with the observed and extrapolated ionizing spectrum. ------------------------------------------------------------------------------------ 8. Additional comments or special requests. When our HST observing dates become known, we will request nearly simultaneous time at Lick and Keck Observatories to obtain optical spectra and images, IR images, and IR spectra. These data will be combined with the UV spectra to construct an overall continuum spanning a large wavelength range. A complete analysis of the data will subsequently be done. No funds are being requested here to support the ground-based observations. Page 5 ------------------------------------------------------------------------------------ 9. Description of previous HST work. A. V. Filippenko, PI: GO 2590, "Deep Imaging of the Site of SN 1961V, a Possible Extragalactic Eta Carinae Analogue." Not related to this project. A. V. Filippenko, Co-I: GO 3484, "Probing the Nuclear Regions of the Seyfert Galaxy NGC 5548." (PI: B. M. Peterson). Not related to this project. A. V. Filippenko, PI: GO 3507, "UV Spectroscopy and High-Resolution Imaging of NGC 4395, the Least Luminous and Nearest Known Seyfert 1 Nucleus." Not related to this project, but shows that the data quality for Arp 102B should be adequate. (NGC 4395 is comparable to Arp 102B in UV brightness.) A. V. Filippenko, Co-I: GO 3519, "UV Imaging of Nearby Galaxies." (PI: D. Maoz.) Not related to this project. A. V. Filippenko, Co-I: GO 3810, "The Stellar Content of Wolf-Rayet Galaxies." (PI: P. Conti.) Not related to this project. In addition, Filippenko was involved in one of the discoveries made by the QSO Snapshot Survey (PI: J. N. Bahcall.) GO 2590: Data were received a few months ago, and are currently being analyzed. An object has been detected at the position of SN 1961V; color information is being used to determine whether this is the supernova remnant, the surviving "progenitor," or an unrelated object. GO 3507: We recently received the data. Preliminary analysis reveals strong emission lines similar to those of luminous Seyfert 1 nuclei (e.g., C IV 1549, C III] 1909, Mg II 2800) superposed on a weak continuum. The nucleus seems unresolved on a scale of 1 pc (0.1"). Thus, NGC 4395 appears to contain a bona fide Seyfert 1 nucleus, but with an absolute blue magnitude of only -10 --- comparable to very luminous stars Other proposals: Data not obtained yet. "A Gravitational Lens Candidate Discovered with the Hubble Space Telescope." D. Maoz, J. N. Bahcall, D. P. Schneider, R. Doxsey, N. A. Bahcall, A. V. Filippenko, W. M. Goss, O. Lahav, and B. Yanny; Astrophysical Journal (Letters), 386, L1, 1992. ------------------------------------------------------------------------------------ 10. Resources to be supplied by investigator's institution(s). Both U. C. Berkeley and Columbia University have extensive computing facilities (VMS and UNIX) in their Astronomy Departments, as does Los Alamos National Laboratory. Image-processing workstations, graphics terminals, laser printers, large disks, and tape drives are all available. Many computer programs exist for analysis of data. Both universities also have many highly capable graduate students and postdoctoral fellows, some of whom may participate in various aspects of this project. Ground-based complementary observations can readily be obtained (with short notice) at Lick Observatory; proposals for Keck time will also be submitted by the PI. The usual secretarial and technical support is available at Berkeley, Columbia, and Los Alamos. ------------------------------------------------------------------------------------ 11. Address Information Name: ALEXEI V. FILIPPENKO Category: PI Institution: UC-Berkeley Address: DEPARTMENT OF ASTRONOMY 601 CAMPBELL HALL UNIVERSITY OF CALIFORNIA City: BERKELEY State: CA Zip Code: 94720 Country: USA Telephone: 510-642-1813 Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 4635c [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 ARP102B E,303,315,320,910 RA = 17H 17M 56.34S +/- 1950.0 Z = 1 V = 16.0 +/- 0.3 0.04S, 0.02438 2 B-V = 1.0 +/- 0.2 DEC = +49D 01' 49.6" +/- 3 F-CONT(1400) = 7.6 +/- 2.3 E-16 0.6" 4 F-CONT(1700) = 1.0 +/- 0.3 E-15 5 F-CONT(2300) = 1.0 +/- 0.3 E-15 Comments: MAGNITUDES AND FLUXES REFER TO NUCLEUS ONLY. BRIGHT NUCLEUS SUPERPOSED ON FAINTER GALAXY BACKGROUND. PI HAS COMPARED THESE COORDS TO GASP, AND PREFERS THESE. - 2/11/93 ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 4635c [ 7] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 ARP102B FOS/RD ACQ/ 4.3 MIRROR 1 1S 1 1 ONBOARD ACQ FOR 2 PEAK 2 SPATIAL SCAN CYCLE 3 / 1-7 GROUP 1-4 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ 2 ARP102B FOS/RD ACQ/ 1.0 MIRROR 1 2S 1 1 ONBOARD ACQ FOR 3- PEAK 2 4 SPATIAL SCAN ------------------------------------------------------------------------------------------------------------------------------------ 3 ARP102B FOS/RD ACCUM 4.3 G270H 2760 1 60M 36 5 1 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 4 ARP102B FOS/RD ACCUM 4.3 G190H 1950 1 143M 23 4 2 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ 5 ARP102B FOS/BL ACQ/ 4.3 MIRROR 1 8S 1 3 ONBOARD ACQ FOR 6 PEAK 2 SPATIAL SCAN GROUP 5-7 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ 6 ARP102B FOS/BL ACQ/ 1.0 MIRROR 1 12S 1 3 ONBOARD ACQ FOR 7 PEAK 2 SPATIAL SCAN ------------------------------------------------------------------------------------------------------------------------------------ 7 ARP102B FOS/BL ACCUM 4.3 G130H 1380 1 242M 11 3 3 Comments: IF THERE IS EXTRA TIME BEFORE EARTH OCCULTATION NEAR END OF EXPOSURE, CAN INCREASE EXPOSURE TIME TO INCREASE S/N RATIO. ------------------------------------------------------------------------------------------------------------------------------------ Scan Paramters Form Proposal ID: 4635c [ 8] ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 1 Exposure Logsheet lines: 1,5 FGS Scan: DWELL Dwell Only: dwell points/line: 3 Seconds per dwell: 1.00 Scan width (arc-secs): 0.0000 Scan length (arc-secs): 2.8000 Angle between sides (degrees) 90.00 Number of lines: 1 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 0.000 Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 1.4000 Width Offset (arc-sec): 0.0000 ------------------------------------------------------------------------------------------------------------------------------------ Data ID: 2 Exposure Logsheet lines: 2,6 FGS Scan: DWELL Dwell Only: dwell points/line: 6 Seconds per dwell: 1.00 Scan width (arc-secs): 0.7000 Scan length (arc-secs): 3.5000 Angle between sides (degrees) 90.00 Number of lines: 2 Scan rate (arc-sec/sec): 0.0000 PA of first scan line (degrees) 90.000 Scan frame (CEL or S/C): S/C Length Offset (arc-sec): 1.7500 Width Offset (arc-sec): 0.3500 ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 4635c [ 9] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations FOS/RD FOS/BL ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACQ/PEAK ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 7.47 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category QUASARS & AGN ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category RADIO GALAXIES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ONBOARD ACQ FOR 2; SPATIAL SCAN; CYCLE 3 / 1-7; GROUP 1-4 NO GAP; ONBOARD ACQ FOR 3-4; ONBOARD ACQ FOR 6; GROUP 5-7 NO GAP; ONBOARD ACQ FOR 7; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements MIRROR G270H G190H G130H ------------------------------------------------------------------------------------------------------------------------------------ Target Names ARP102B ------------------------------------------------------------------------------------------------------------------------------------