! File: 3623C.PROP ! Database: PEPDB ! Date: 19-FEB-1994:14:14:09 coverpage: title_1: THE CENTRAL STAR CLUSTER OF THE GALAXY: DEEP IMAGING sci_cat: STELLAR POPULATIONS sci_subcat: GALACTIC CENTER proposal_for: GO pi_fname: KWOK-YUNG pi_lname: LO pi_inst: UNIVERSITY OF ILLINOIS pi_country: USA pi_phone: 217-333-9381 hours_pri: 3.11 num_pri: 1 wf_pc: Y funds_amount: 90979 funds_length: 12 off_fname: HARVEY off_mi: J. off_lname: STAPLETON off_title: SECR. CAMPUS RES. off_inst: UNIVERSITY OF ILLINOIS off_addr_1: 506 S. WRIGHT STREET off_city: URBANA off_state: IL off_zip: 61801 off_country: USA off_phone: 217-333-0037 ! end of coverpage abstract: line_1: We propose to use the HST Wide Field Camera to obtain deep images of the line_2: Galactic center with 0.1" (850 AU at 8.5 kpc) resolution at 1.03 micron line_3: wavelength. Recent observations have revealed a multitude of unusual line_4: phenomena at the center, suggesting that the Galactic center may be a line_5: low energy version of an active galactic nucleus and may harbor a line_6: massive collapsed object. Unambiguous delineation of the central star line_7: cluster, which would provide an important constraint on the central line_8: mass distribution, has been hampered by the inadequate angular line_9: resolution of ground-based observations. A 20 min. HST observation by line_10: us has already detected components of IRS16, which has been the focus line_11: of previous efforts to define the central star cluster. The proposed line_12: observation will map the structure of IRS16 in much greater detail. line_13: The resolution and sensitivity of the proposed observations can also line_14: detect and resolve individual K and M gaint stars of the central star line_15: cluster, despite the large visual extinction to the center; several line_16: late M giants may already be detected by the previous HST data. line_17: Understanding the nearest galactic nucleus will be important for the line_18: interpretation of more energetic active galactic nuclei. ! ! end of abstract general_form_proposers: lname: LO fname: KWOK-YUNG title: PI inst: UNIVERISTY OF ILLINOIS country: USA ! lname: BIRETTA fname: JOHN mi: A. inst: NATIONAL RADIO ASTRONOMY OBSERVATORY country: USA ! ! end of general_form_proposers block general_form_text: question: 2 section: 1 line_1: We propose to obtain a total exposure of 11200 sec. with the Wide Field line_2: Camera of the Galactic Center (IRS16) through the F1042M filter (center line_3: wavelength 1.0326 microns). The exposure will be divided in to 16 line_4: sub-exposures to aid in identification of cosmic ray events. Two different line_5: positionings of the target on the detector will be used to help distinguish line_6: faint objects from any detector artifacts. ! question: 2 section: 2 line_1: Cycle 1 Primary Hours: Parallel Hours: Exposures: line_2: Cycle 2 Primary Hours: 3.11 Parallel Hours: Exposures: 16 line_3: Cycle 3 Primary Hours: Parallel Hours: Exposures: line_4: Cycle 4 Primary Hours: Parallel Hours: Exposures: ! question: 3 section: 1 line_1: The primary reason to use HST is its unique capability of high resolution. The line_2: 0.1" resolution makes it possible to image directly the structure of IRS16, line_3: and to resolve and detect the individual stars of the central star cluster of line_4: the Galaxy. line_6: Imaging of the Galactic central star cluster has been attempted from the line_7: ground in the 1 - 2 micron range by various groups including ourselves line_8: (Biretta, Lo, and Young 1982). Emphasis has been placed on resolving IRS16, line_9: a very bright near-IR source suspected to mark the location of the central star line_10: cluster. Lunar occultation observations at 2 microns have resolved IRS16 line_11: into 3 point sources (<0.05") and extended components (~0.3"), but a direct line_12: image at 0.1" resolution is not available. Recent images at 1 micron with line_13: 0.5" resolution (Rosa et al. 1991) partially resolve the structure of IRS16, line_14: but individual giant stars are not detected, and the relationship of IRS16 line_15: to the central cluster remains unclear. line_17: A 20 min. HST PC exposure obtained by us on 10 July 1991 (Fig 1.) has found line_18: two extended (~0.3 arcsec) components in IRS16, and detected other 2 micron line_19: infrared sources. There is also a large excess of 4 to 5 sigma features with line_20: sizes <0.3", which is consistent with detection of late-type gaint stars in the line_21: central star cluster. The detection of small structures within IRS16, and line_22: evidence for detection of giant stars, indicates the power of HST's resolving line_23: capabilities. ! question: 4 section: 1 line_1: The exposure time requested is based on the sensitivity required to detect line_2: individual gaint stars at the Galactic center, and is based on comparisons line_3: with ground based and previous HST observations. Based on the 2.2 micron line_4: extinction of 3 mag. within the central 1 arcmin of the Galactic center line_5: (M. Rieke, private comm.; see also Sellgren et al. 1986) and a distance of line_6: 8 kpc, the requested exposure time will detect a K5III, an M0III, and an line_7: M5III star with a S/N ratio of 5, 11, and 25, respectively. Given the line_8: expected number of giant stars of <100 per 6.5 arcsec aperture, the line_9: observations should not be confusion limited. line_11: Our previous 20 min. HST PC exposure through this filter has detected line_12: components of IRS16 at the 4 to 6 sigma level, as well as other Galactic line_13: center IR sources. In addition, several previously unidentified point line_14: sources are detected at the 4 to 5 sigma level, which is consistent with line_15: the expected detection of late MIII stars. The proposed observations will line_16: give a factor of 7 improvement in S/N ratio due to longer exposure, and use of line_17: WFC instead of PC. line_19: Differences from Phase I (5 x 2400 sec. PC exposures) are due to evidence line_20: for faint tails on cosmic ray hits in our Cycle 1 images. These effectively line_21: triple the area affected by c.r. hits, requiring more images for c.r. rejection line_22: (16 x 700 sec.), which increases net read-out noise. To regain necessary SNR, line_23: we will use WFC instead of PC, at some sacrifice in deconvolution capability. ! question: 5 section: 1 line_1: (none) ! question: 5 section: 2 line_1: (none) ! question: 6 section: 1 line_1: The 16 data frames will be calibrated in the standard fashion. If on-orbit line_2: flats are not available, Thermal Vaccuum test flats could be used after line_3: adjustment for low spatial frequency illumination problems. Each set of 8 line_4: frames will be combined to eliminate cosmic ray events. The two resulting line_5: images from the two pointings will be compared to distinguish detector artifacts line_6: from faint objects, and then finally summed. Light from the PSF wings of line_7: bright objects will be reduced by subtracting scaled images of the PSF; several line_8: bright, uncrowded stars are available in the images for PSF determination. line_10: Since the extinction to the Galactic center varies strongly with wavelength line_11: (A[1.03 microns]=10.7 mag. vs. A[0.87 microns]=13.7 mag.), we will use line_12: existing 0.87 micron HST PC images to distinguish foreground objects from line_13: those at the Galactic center (cf. Biretta, Lo, and Young 1982). line_15: The 1.03 micron image will then be used to study the structure of the central line_16: 2 pc (~30") of the Galaxy. Magnitudes and sizes of features will be measured. line_17: If the extended background seen at 2 microns is caused by giant stars, we can line_18: expect to resolve this emission into perhaps several hundred stars. The line_19: distribution of such point sources will be studied to better define the dynamic line_20: center of the central star cluster, its core radius, and to look for the line_21: existence of a cusp caused by a massive collapsed object. In addition, we will line_22: determine directly the structure of the IRS16 complex, and its relation to the line_23: dynamic center and the compact nonthermal radio source. ! question: 7 section: 1 line_1: (none) ! question: 8 section: 1 line_1: GO program P2459, "The Central Star Cluster of the Galaxy;" directly related line_2: to present proposal. ! question: 8 section: 2 line_1: Several of the Galactic center infrared sources have been detected at the line_2: 4 to 6 sigma level (of the background noise), including IRS16, which is line_3: thought to be associated with the central star cluster. There is also line_4: a large excess of 4 to 5 sigma features, which is consistent with detection line_5: of individual late M gaint stars in the central cluster. ! question: 8 section: 3 line_1: (Paper in preparation.) ! question: 9 section: 1 line_1: The extensive image processing facilities of the Laboratory for Astronomical line_2: Imaging at the University of Illinois, and facilities at the National Radio line_3: Astronomy Observatory, will be available for reduction and analysis of the line_4: HST data. The academic year salary of the PI is paid by the University of line_5: Illinois. ! !end of general form text general_form_address: lname: LO fname: KWOK-YUNG category: PI inst: UNIVERSITY OF ILLINOIS addr_1: DEPARTMENT OF ASTRONOMY addr_2: 1002 W. GREEN STREET city: URBANA state: IL zip: 61801 country: USA phone: 217-333-9381 telex: 217-244-7638 ! ! end of general_form_address records fixed_targets: targnum: 1 name_1: IRS16-POS1 name_2: GALACTIC-CENTER-POS1 name_3: SGR-A-POS1 descr_1: E,301,312,910, descr_2: I,601, descr_3: C,202 pos_1: RA = 17H 42M 29.335S +/- 0.07S, pos_2: DEC = -28D 59' 18.6" +/- 1.0" equinox: 1950.0 comment_1: TARGET 1 AND 2 ARE TWO POSITIONINGS comment_2: OF THE PROGRAM OBJECT ON THE comment_3: DETECTOR. CARE SHOULD BE TAKEN TO comment_4: INSURE THE OBJECT FALLS ON GOOD comment_5: AREAS OF THE DETECTOR FOR BOTH comment_6: POSITIONINGS. THE PROGRAM OBJECT comment_7: IS AT RA=17H 42M 29.335S, comment_8: DEC=-28D 59' 18.6", EQUINOX 1950. comment_9: AN OFFSET OF 7" +/- 1" ALONG NW-SE comment_10: LINE IS DESIRED BETWEEN POSITIONS. fluxnum_1: 1 fluxval_1: I=22.5+/-0.5, TYPE=K0III, A(V)=30 fluxnum_2: 2 fluxval_2: F(9800) = 8 +/- 4 E-21 fluxnum_3: 3 fluxval_3: SIZE = 0.3 +/- 0.3 ! targnum: 2 name_1: IRS16-POS2 name_2: GALACTIC-CENTER-POS2 name_3: SGR-A-POS2 descr_1: E,301,312,910, descr_2: I,601, descr_3: C,202 pos_1: RA-OFF = 0.38S +/- 0.08S, pos_2: DEC-OFF = -5.0" +/- 1.0", pos_3: FROM 1 equinox: 1950.0 comment_1: SEE TARGET 1 COMMENT fluxnum_1: 1 fluxval_1: I=22.5+/-0.5, TYPE=K0III, A(V)=30 fluxnum_2: 2 fluxval_2: F(9800) = 8 +/- 4 E-21 fluxnum_3: 3 fluxval_3: SIZE = 0.3 +/- 0.3 ! ! end of fixed targets ! No solar system records found ! No generic target records found exposure_logsheet: linenum: 1.000 targname: IRS16-POS1 config: WFC opmode: IMAGE aperture: WF1 sp_element: F1042M num_exp: 8 time_per_exp: 700S s_to_n: 20 s_to_n_time: 11200S fluxnum_1: 1 fluxnum_2: 2 fluxnum_3: 3 priority: 1 param_1: CR-SPLIT=NO, param_2: PRE-FLASH=YES, param_3: CLOCKS=NO req_1: CYCLE 2 ! linenum: 2.000 targname: IRS16-POS2 config: WFC opmode: IMAGE aperture: WF1 sp_element: F1042M num_exp: 8 time_per_exp: 700S s_to_n: 20 s_to_n_time: 11200S fluxnum_1: 1 fluxnum_2: 2 fluxnum_3: 3 priority: 1 param_1: CR-SPLIT=NO, param_2: PRE-FLASH=YES, param_3: CLOCKS=NO req_1: CYCLE 2 ! ! end of exposure logsheet ! No scan data records found