! Proposal 6655, submission 1 ! PI: Andrew M. Smith ! Received Thu Feb 1 16:13:51 EST 1996 ! From: guest@hrssun.gsfc.nasa.gov ! Hubble Space Telescope Cycle 6 (1996) Phase II Proposal Template ! ! Proposal_Information ! Section 4 Title: SEARCH FOR INTERSTELLAR CH_2 IN THE SPECTRUM OF HD 154368 Proposal_Category: GO Scientific_Category: INTERSTELLAR MEDIUM Cycle: 6 Investigators PI_name: Andrew M. Smith PI_Institution: The Goddard Space Flight Center CoI_Name: Frederick Bruhweiler CoI_Institution: The Catholic University of America Contact: ! Y or N (designate at most one contact) CoI_Name: Cheng-Hsuan Lyu CoI_Institution: STX-Hughes Contact: ! Y or N (designate at most one contact) Abstract: ! Free format text (please update) We propose to search for the important interstellar molecule, CH_2, which is predicted to be very abundant in theoretical models of gas phase chemistry in diffuse and translucent clouds, but which has not yet been detected. Our goal is to detect the absorption band spectrum in the wavelength interval extending from 139 nm to 142 nm to both establish the presence of CH_2 and to clarify details in the possible reaction channels leading to the abundant and often observed molecule, CH. The target star is HD 154368 (O9.5Iab; 6.1 m_V) which exhibits a well observed interstellar molecular spectrum. IUE observations show a locally smooth continuum at the locations of the CH_2 bands, and indicate that significant conclusions can be made with an exposure time of 258 minutes. Questions ! Free format text (please update) Observing_Description: We will obtain a medium resolution spectrum of HD 154368 with the GHRS using the G160M grating. The spectrum will be centered on the diode array so that the CO 4,0 vibrational band at 141.9nm and the CH_2 band at 139.68nm will be recorded simultaneously. Since the interstellar spectrum is well observed at optical and radio wavelengths we will only observe the UV spectrum in this one band. The CO band will be saturated, but a velocity dispersion determined from radio measurements together with the band equivalent width will permit us to derive a CO column density, which can be used to compare our results with other observations. We estimate that use of the N2 acqusition mirror will yield a count rate per pixel of 289,600 counts/second. (The star is bright at V=6.1, but it is heavily reddened with E(B-V)=0.82). A 0.2 second integration time yields a count per pixel of 57,920. Thus, a standard target acqusition time of 11 minutes is in order. We plan to use the large aperture, the FP-SPLIT=STD, STEP-PATT=5, COMB=4 options, and the same initial carrousel position for each exposure. After reconstituting the spectrum from all the FP-SPLIT subspectra the spectra will be re-binned in a 2 to 1 or even larger ratio. This is done to increase the S/N in a situation where intrinsic resolution can be sacrificed to a limited extent. The 141.45nm feature we are trying to detect is about 0.05nm wide and is thus oversampled by approximately 10 pixels. Tomographic techniques developed by our group (Lyu, Bruhweiler, and Smith 1995) will be used to reduce the effects of fixed pattern noise in our data. Taking into account the guide star aquisition (7.5 min, 6 min), the target acquisition (11 min) and the ACCUM mode overhead (4 min) leads to an 8 orbit visit in order to obtain 258 minutes of on-target observing time. Since we will observe the 4,0 band of the CO A-X system and the S I resonance line at 140.15 nm we do not need a WAVECAL. These interstellar features will provide adequate fiducials to align the subexposures of the FT-SPLIT procedure. We will have to use the GHRS capability to pause an observation across orbits to obtain our exposure time objective within the 8 orbit limit. High signal-to-noise is crucial. This implies a need for the best possible counting statistics. Hence, minimum impact from the SAA is highly desirable. Real_Time_Justification: There are no special requirements for this observation. No supporting observations are required. Calibration_Justification: Special calibrations are not required for this observation. Additional_Comments: Fixed_Targets ! Section 5.1 Target_Number: 1 Target_Name: HD154368 Alternate_Names: BD-35D11306 Description: STAR,Supergiant O Position: RA=17H 06M 28.40S +/- 0.02S, ! Most common specification format is DEC=-35D 27' 03.9" +/- 0.2" ! RA=0H 0M 0.00S +/- 0S, ! DEC=0D 0' 0.0" +/- 0", ! PLATE-ID=0000 Equinox: 2000 RV_or_Z: V=+13 RA_PM: +0.0007 ! Units are seconds of time per year Dec_PM: -0.002 ! Units are seconds of arc per year Epoch: 2000 Annual_Parallax: Flux: V=6.13 +/-0.03 ! Include at least V and B-V TYPE=O9.5Iab B-V=+0.48 +/- 0.03 E(B-V)=0.82 +/- 0.04 F(1414)=8.0+/-0.8E-12 Comments: Flux from IUE observation, SWP 41365 Visits ! Section 6 Visit_Number: 1 Visit_Comments: Assume one visit, eight contiguous orbits. The following program occupies eight full orbits with twelve 1740.8s exposures and one 544.0s exposure. The last exposure consists of five FT-SPLIT cycles each 108.8s in duration. The available time in the final (eighth) orbit is 0.8s short of including a 6th FT-SPLIT cycle. It is hoped that by creative scheduling a 6th FT-SPLIT cycle can be included in the final exposure. Exposure_Number: 1 ! Section 6.5 Target_Name: HD154368 Config: HRS Opmode: ACQ Aperture: 2.0 Sp_Element: MIRROR-N2 Wavelength: Optional_Parameters: BRIGHT=RETURN SEARCH-SIZE=3 Number_of_Iterations: 1 Time_Per_Exposure: 1.8S Special_Requirements: ONBOARD ACQ FOR 2-5 ! Section 7.2 Comments: STEP-TIME = 0.2 S Exposure_Number: 2 ! Section 6.5 Target_Name: HD154368 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1408.0 Optional_Parameters: FP-SPLIT=STD, STEP-PATT=5, COMB=FOUR Number_of_Iterations: 6 Time_Per_Exposure: 1740.8 S Special_Requirements: ! Section 7.2 Exposure_Number: 3 ! Section 6.5 Target_Name: HD154368 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1408.0 Optional_Parameters: FP-SPLIT=STD, STEP-PATT=5, COMB=FOUR, SPYBAL=YES Number_of_Iterations: 1 Time_Per_Exposure: 1740.8 S Special_Requirements: ! Section 7.2 Exposure_Number: 4 ! Section 6.5 Target_Name: HD154368 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1408.0 Optional_Parameters: FP-SPLIT=STD, STEP-PATT=5, COMB=FOUR Number_of_Iterations: 5 Time_Per_Exposure: 1740.8 S Special_Requirements: ! Section 7.2 Exposure_Number: 5 ! Section 6.5 Target_Name: HD154368 Config: HRS Opmode: ACCUM Aperture: 2.0 Sp_Element: G160M Wavelength: 1408.0 Optional_Parameters: FP-SPLIT=STD, STEP-PATT=5, COMB=FOUR Number_of_Iterations: 1 Time_Per_Exposure: 544.0 S Special_Requirements: ! Section 7.2 Data_Distribution ! Defaults indicated; change if desired Medium: 8MM ! 8MM or 6250BPI or 1600BPI Blocking_Factor: 10 ! 10 or 1 ! Only astronomers with very old 9- ! track tape drives should consider ! a blocking factor of 1 Ship_To: PI_Address ! STSCI or PI_Address or ! PI Address from Phase I is: ! ! Code 681 ! Greenbelt ! 20771 ! ! Ship_Via: UPS ! UPS (2-day) or OVERNIGHT ! Overnight shipping done at PI expense Recipient_Email: ! Needed if Ship_To: is not PI_Address !