Space Telescope Fine Guidance Research Articles

Constraints on the origin of the massive, hot, and rapidly rotating magnetic white dwarf RE J 0317-853 from an HST parallax measurement

We use the parallax measurements of RE J 0317-853 to determine its mass, radius, and cooling age and thereby constrain its evolutionary origins. We observed RE J 0317-853 with the the Hubble Space Telescope's Fine Guidance System to measure the parallax of RE J 0317-853 and its binary companion, the non-magnetic white dwarf LB 9802. In addition, we acquired spectra of comparison stars with the Boller & Chivens spectrograph of the SMARTS telescope to correct the parallax zero point. For the corrected parallax, we determine the radius, mass, and the cooling age with the help of evolutionary models from the literature. The properties of RE J 0317-853 are constrained using the parallax information. We discuss the different cases of the core composition and the uncertain effective temperature. We confirm that RE J 0317-853 is close to the Chandrasekhar's mass limit in all cases and almost as old as its companion LB 9802. The precise evolutionary history of RE J 0317-853 depends on our knowledge of its effective temperature. It is possible that it had a single star progenitor possible if we assume that the effective temperature is at the cooler end of the possible range from 30000 to 50000; if T_eff is instead at the hotter end, a binary-merger scenario for RE J 0317-853 becomes more plausible.

Calibrating cosmological chronometers: White dwarf masses via astrometry

In an effort to increase the number of accurate dynamical masses for white dwarfs (WDs), we have begun an initiative using Hubble Space Telescope's Fine Guidance Sensors (FGS) to resolve suspected binary WDs. With the increasing number of WD trigonometric parallaxes becoming available via CTIO's and the USNO's ongoing parallax programs, we have targeted objects that are overluminous at V magnitude and are presumably unresolved multiple systems. A few targets were selected because of spectral anomalies or possible perturbations evident in the residuals of the trigonometric parallax solutions. A total of 16 HST orbits were designated to this program and 12 are completed. Of the eleven WDs observed thus far (one object was observed twice), all but one were unresolved. Analysis of a recent orbit's data indicate a pair was resolved with a separation of 70 mas and a delta V magnitude of ∼1.4. Coupled with astrometric data from the USNO parallax program, we have obtained preliminary constraints on component masses.

Resolving OB Systems in the Carina Nebula with theHubble Space TelescopeFine Guidance Sensor

We observed 23 OB stars in the Carina Nebula (NGC 3372) with the Hubble Space Telescope's Fine Guidance Sensor 1r (FGS1r) in its high angular resolution mode. Five of these OB stars are newly resolved binaries with projected separations ranging from 0015 to 0352 (37 to 880 AU at a distance of 2.5 kpc), and V-band magnitude differences ranging from 0.9 to 2.8. The most important astrophysical result is the unexpected resolution of the prototype O2 If* star HD 93129A as a 55 milliarcsecond (mas) double with a ΔmV of 0.9. This object has served as a spectroscopic benchmark for the analysis of the most massive hot stars and their winds on the prior assumption that it is a single star. This discovery supports the interpretation of recent radio and X-ray observations as evidence of colliding-wind phenomena in HD 93129A. Another interesting result is the determination of an upper limit of about 35 AU for the projected separation of the binary pairs in the hierarchical double spectroscopic binary HD 93206. The high incidence of resolved binaries provides motivation for a more thorough, statistically meaningful study of multiplicity among the most massive stars in the young ionizing clusters of the nebula to obtain a complete sample of the long-period systems that have evaded spectroscopic detection. However, considering that the nine spectroscopic binaries with accurate orbits in the Carina Nebula have orbital dimensions 1 AU, which at a distance of 2.5 kpc subtends an angle of only 0.4 mas, well below the 10 mas angular resolution of FGS1r, there remains a significant range of orbital periods and separations over which it is very difficult to detect multiplicity in the nebula with currently available instruments.

The First Definitive Binary Orbit Determined with the [ITAL]Hubble[/ITAL] [ITAL]Space[/ITAL] [ITAL]T[/ITAL][ITAL]elescope[/ITAL] Fine Guidance Sensors: Wolf 1062 (Gliese 748)

The M dwarf binary, Wolf 1062 (Gliese 748), has been observed with the Hubble Space Telescope (HST) Fine Guidance Sensor 3 in the transfer function scan mode to determine the apparent orbit. This is the first orbit defined fully and exclusively with HST, and is the most accurate definitive orbit for any resolved, noneclipsing system. The orbital period is 2.4490 ± 0.0119 yr and the semimajor axis is 01470 ± 00007—both quantities are now known to better than 1%. Using the weighted mean of seven parallax measurements and these HST data, we find the system mass to be 0.543 ± 0.031 M⊙, where the error of 6% is due almost entirely to the parallax error. An estimated fractional mass from the infrared brightness ratio and infrared mass-luminosity relation yields a mass for the primary of 0.37 M⊙, and the secondary falls in the regime of very low mass stars, with a mass of only 0.17 M⊙.

HST-FGS parallaxes of two high-velocity stars.

view Abstract Citations (6) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS HST-FGS parallaxes of two high-velocity stars. MacConnell, D. Jack ; Osborn, Wayne H. ; Miller, Richard J. Abstract Astrometric position measurements with the Hubble Space Telescope's Fine Guidance System have been used to measure the trigonometric parallaxes of two high-velocity stars, R50 = G166-37 and W624 = G16-25. In both cases, the parallaxes are small and confirm large velocities in the galactocentric rest frame. We derive pi_ {abs} = 5.2 +/- 0.7 mas and vrf = 467 kms for R50. The results for W624 are pi_ {abs} = 3.8 +/- 1.0 and vrf = 326 kms with an uncertainty of about 30%. Our results support a value for the galactic escape velocity at the solar distance of about 475 kms. Publication: The Astronomical Journal Pub Date: September 1997 DOI: 10.1086/118560 Bibcode: 1997AJ....114.1268M Keywords: ASTROMETRY full text sources ADS | data products SIMBAD (11) MAST (1) ESA (1)

The Guide Star Selection System and the Guide Star Catalog for Space Telescope

The Guide Star Selection System (GSSS) will provide relative positions of two guide stars and the target for each observation of the Space Telescope as well as photometry for the guide stars. Being developed at the Space Telescope Science Institute, the GSSS is a production system which is based on PDS measurements of Schmidt survey plates. The specified accuracy for the system is +/−0.33 arcsec for the separation of the guide stars and 0.4 mag in the bandpass of the Space Telescope's Fine Guidance Sensors. The GSSS will produce two catalogs which will be used in the operation of the system. The Guide Star Photometry catalog includes photoelectric measurements (+/−0.05 mag) in B and V for six stars over the guide star range, 9.0 to 14.5 visual magnitude, near the central part of each 6 by 6 deg survey plate. The Guide Star Catalog will include the list of all possible guide stars and brighter, positions (at least +/−1 arcsec) and magnitudes (at least +/−0.4 mag) for essentially the whole sky complete to visual magnitude 15.