Proposal_Information Title: The Masses of the O-type Binary 15 Monocerotis Proposal_Category: GO Scientific_Category: BINARIES AND STAR FORMATION Cycle: 6 Investigators PI_Name: Dr. Douglas Gies PI_Institution: Georgia State University CoI_Name: Dr. W. Hartkopf CoI_Institution: Georgia State University Contact: N CoI_Name: Dr. B. Mason CoI_Institution: Georgia State University Contact: N CoI_Name: Dr. W. Bagnuolo CoI_Institution: Georgia State University Contact: N Abstract: The O-type star 15 Mon (HD 47839) was recently discovered to be a speckle and spectroscopic binary with an orbital period of 25 years. An analysis of both the radial velocity curve and astrometric orbit yields the masses of the components and distance to the system. Both radial velocity and astrometric measurements are scant at present, but the system is now approaching periastron (1998.8) and continued spectroscopic and astrometric monitoring will lead to a definitive orbit and yield important information about the masses of O-type stars. FGS measurements of separation, position angle, and magnitude difference are needed to bridge the gap between current speckle observations and the next generation of optical interferometers. Questions Observing_Description: This is a Continuation Proposal for a long term program which was approved in Cycle 5 for 2 orbits in each of Cycles 5, 6, and 7. Our goal is to obtain FGS TRANS mode measurements of the separation, position angle, and magnitude difference of 15 Mon once each year over the current and next observing cycles. We are aiming for a positional accuracy of a few mas and a photometric accuracy of 0.1 mag, both of which have been achieved in recent binary studies with the FGS (see Franz et al. 1992, in Complementary Approaches to Double and Multiple Star Research, ASP Conf. Series 32, ed. McAlister & Hartkopf, San Francisco: ASP, 369). Because of the relative brightness of the star, the observations will be made with the 5 mag neutral density filter, F5ND. We plan to obtain approximately 16 scans in the TRANS mode of operation which should require less than 34 minutes exposure time. We will make observations with a scan orientation of ~ 45 degrees to the predicted binary position angle in order to optimize the transfer function in both x and y axes. We estimate that an observation of 15 Mon can easily be accomplished in a single orbit. The Cycle 5 observation was made on 1996 January 26. The Transfer Function (TF) of the FGS with the F5ND filter needs to be well determined to analyze the observations, so we also request a single orbit to observe a reference single star (of similar brightness and color as 15 Mon) in conjunction with each observation of the main target. This reference TF will be used in the data reduction procedure to extract accurately the binary components in the composite TF of 15 Mon (see Lattanzi et al. 1992, in Complementary Approaches to Double and Multiple Star Research, ASP Conf. Series 32, ed. McAlister & Hartkopf, San Francisco: ASP, 377). The calibration TF needs to made at the same reference position, with the same neutral density filter, for a single star with approximately the same flux distribution as our main target. We have selected the star Mu Col (HD38666, HR1996; spectral type O9.5V) as our calibration source. This star has a similar magnitude and color as 15 Mon, and appears to be a truly single star. There are no known visual companions, and we have found no evidence of a companion in multiple observations made with the CHARA speckle camera at the KPNO 4-m telescope. We need to obtain calibration scans in the same way and at about the same time as the 15 Mon scans. Real_Time_Justification: None Our group (plus collaborators) will be continuing a program of high S/N spectroscopy of 15 Mon over the next decade to derive an accurate radial velocity curve and mass ratio. The spectra will be obtained primarily with our Multiple- Telescope Telescope (at the GSU Hard Labor Creek Observatory near Atlanta), a 1-m equivalent aperture telescope with a fiber-fed spectrograph and CCD detector. Calibration_Justification: See "Observing_Description" section above. Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: HD47839 Alternate_Names: SAO114258,HR2456 Description: STAR, MAIN SEQUENCE O Position: RA=6H 38M 13.429S +/- 0.035S,DEC=09D 56' 37.02" +/- 0.15" Equinox: B1950 RV_or_Z: V = 22.0 RA_PM: 0.0001 Dec_PM: -0.007 Epoch: B1950 Annual_Parallax: 0.001 Flux: V = 4.65+/-0.02 B-V = -0.25+/-0.02 TYPE=O7V((F)) Comments: LONG PERIOD BINARY Target_Number: 2 Target_Name: HD38666 Alternate_Names: SAO196149,HR1996 Description: STAR, MAIN SEQUENCE O Position: RA=5H 44M 08.324S +/- 0.013S,DEC=-32D 19' 27.47" +/- 0.18" Equinox: B1950 RV_or_Z: V = 109. RA_PM: 0.0003 Dec_PM: -0.025 Epoch: B1950 Annual_Parallax: 0.000 Flux: V = 5.17+/-0.02 B-V = -0.28+/-0.02 TYPE=O9.5V Comments: SINGLE STAR, CALIBRATION TARGET Solar_System_Targets Generic_Targets Scan_Data Visits Visit_Number: 01 Visit_Requirements: ORIENT 221D TO 260D On_Hold_Comments: Visit_Comments: Exposure_Number: 1 Target_Name: HD47839 Config: FGS Opmode: TRANS Aperture: PRIME Sp_Element: F5ND Wavelength: Optional_Parameters: SCANS=7,STEP-SIZE=0.6 Number_of_Iterations: 1 Time_Per_Exposure: 2125S Special_Requirements: POS TARG 0,0 Comments: 17000 SAMPLES PER SCAN Visit_Number: 02 Visit_Requirements: GROUP 1-2 WITHIN 24H On_Hold_Comments: Visit_Comments: Exposure_Number: 1 Target_Name: HD38666 Config: FGS Opmode: TRANS Aperture: PRIME Sp_Element: F5ND Wavelength: Optional_Parameters: SCANS=7,STEP-SIZE=0.6 Number_of_Iterations: 1 Time_Per_Exposure: 2125S Special_Requirements: POS TARG 0,0 Comments: 17000 SAMPLES PER SCAN, CALIBRATION TARGET Data_Distribution ! 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