Proposal_Information Title: The Masses of the O-type Binary 15 Monocerotis Proposal_Category: GO Scientific_Category: Hot Stars Cycle: 5 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: Mr. 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 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: 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 next three 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 10 scans in the TRANS mode of operation which should require less than 10 minutes exposure time. Because the orbit is still loosely defined, we wish to make observations at two scan orientations in the sky to yield high accuracy in the derived positions. This will require a spacecraft roll of less than 30 degrees. According to the Cycle 5 Phase I Proposal Instructions, such a manuever counts as a separate visit, but according to FGS Scientist Larry Taff (STScI), the roll manuever and two sets of scans should require no more than the 52 minutes of visibility during one orbit, so we estimate that an observation of 15 Mon can be accomplished in a single orbit. The Transfer Functions (TF) of the FGS with the F5ND filter have not yet been fully calibrated by STScI scientists, so we also request a single orbit to observe a reference single star, HR1399 (of similar brightness and color as 15 Mon), in conjunction with each observation of the main target. The reference TF will be used in the data reduction to accurately extract 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). 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: ! Move appropriate text from Real_Time_Justification Additional_Comments: Fixed_Targets Target_Number: 1 Target_Name: HD47839 Alternate_Names: 15MON, S-MON, HR2456, SAO114258 Description: STAR, MAIN SEQUENCE O Position: RA=06H 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: HD28149 Alternate_Names: 72TAU, HR1399, SAO76613 Description: STAR, B6-B9.5 V-IV Position: RA=4H 24M 17.800S +/- 0.013S, DEC=+22D 53' 07.12" +/- 0.18" Equinox: B1950 RV_or_Z: V = 13.7 RA_PM: 0.0005 Dec_PM: -0.015 Epoch: B1950 Annual_Parallax: 0.007 Flux: V = 5.53 +/- 0.02, B-V = -0.10 +/- 0.02, TYPE = B7V Comments: SINGLE STAR, CALIBRATION TARGET Visits Visit_Number: 1 Visit_Requirements: ORIENT 52D TO 72D On_Hold_Comments: Visit_Comments: ORIENTATIONS AT 90D, 180D, 270D TO ABOVE ACCEPTABLE Exposure_Number: 1 Target_Name: HD47839 Config: FGS Opmode: TRANS Aperture: 3 Sp_Element: F5ND Wavelength: Optional_Parameters: SCANS=14, STEP-SIZE=0.3, DATA-RATE=32 Number_of_Iterations: 1 Time_Per_Exposure: 1750S Special_Requirements: POS TARG 0,0 Comments: 5000 SAMPLES PER SCAN Visit_Number: 2 Visit_Requirements: ON HOLD On_Hold_Comments: PENDING DECISION AS STSCI CALIBRATION TARGET Visit_Comments: Exposure_Number: 1 Target_Name: HD28149 Config: FGS Opmode: TRANS Aperture: 3 Sp_Element: F5ND Wavelength: Optional_Parameters: SCANS=14, STEP-SIZE=0.3, DATA-RATE=32 Number_of_Iterations: 1 Time_Per_Exposure: 1750S Special_Requirements: POS TARG 0,0 Comments: 5000 SAMPLES PER SCAN, CALIBRATION TARGET Data_Distribution Medium: 8MM Blocking_Factor: 10 Ship_To: PI_Address Ship_Via: UPS Recipient_Email: