ASTROMETRY WITH THE HUBBLE SPACE TELESCOPE: TRIGONOMETRIC PARALLAXES OF SELECTED HYADS

Journal Article · Sun May 15 04:00:00 EDT 2011 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/141/5/172· OSTI ID:21583129

McArthur, Barbara E; Benedict, G Fritz ^[1]; Harrison, Thomas E ^[2]; Van Altena, William ^[3]

---

1. McDonald Observatory, University of Texas, Austin, TX 78712 (United States)
2. Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 (United States)
3. Department of Astronomy, Yale University, New Haven, CT 06520 (United States)

We present absolute parallaxes and proper motions for seven members of the Hyades open cluster, pre-selected to lie in the core of the cluster. Our data come from archival astrometric data from fine guidance sensor (FGS) 3 and newer data for three Hyads from FGS 1r, both white-light interferometers on the Hubble Space Telescope (HST). We obtain member parallaxes from six individual FGS fields and use the field containing van Altena 622 and van Altena 627 (= HIP 21138) as an example. Proper motions, spectral classifications, and VJHK photometry of the stars comprising the astrometric reference frames provide spectrophotometric estimates of reference star absolute parallaxes. Introducing these into our model as observations with error, we determine absolute parallaxes for each Hyad. The parallax of vA 627 is significantly improved by including a perturbation orbit for this previously known spectroscopic binary, now an astrometric binary. Compared to our original (1997) determinations, a combination of new data, updated calibration, and improved analysis lowered the individual parallax errors by an average factor of 4.5. Comparing parallaxes of the four stars contained in the Hipparcos catalog, we obtain an average factor of 11 times improvement with the HST. With these new results, we also have better agreement with Hipparcos for the four stars in common. These new parallaxes provide an average distance for these seven members, (D) = 47.5 pc, for the core, a {+-}1{sigma} dispersion depth of 3.6 pc, and a minimum depth from individual components of 16.0 {+-} 0.9 pc. Absolute magnitudes for each member are compared to established main sequences with excellent agreement. We obtain a weighted average distance modulus for the core of the Hyades of m - M = 3.376 {+-} 0.01, a value close to the previous Hipparcos values, m - M = 3.33 {+-} 0.02.

• OSTI ID: 21583129
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 5 Vol. 141; ISSN 1538-3881
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CALIBRATION
CATALOGS
CLASSIFICATION
DOCUMENT TYPES
INTERFEROMETERS
MEASURING INSTRUMENTS
MOTION
ORBITS
PERTURBATION THEORY
PHOTOMETRY
PROPER MOTION
SPECTROPHOTOMETRY
STARS
TELESCOPES