226 research outputs found
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Hubble Space Telescope Fine Guidance Sensor Parallaxes For Four Classical Novae
We have used data obtained with the Fine Guidance Sensors on the Hubble Space Telescope to derive precise astrometric parallaxes for four classical novae: V603 Aql, DQ Her, GK Per, and RR Pic. All four objects exceeded the Eddington limit at visual maximum. Re-examination of the original light curve data for V603 Aql and GK Per has led us to conclude that their visual maxima were slightly brighter than commonly assumed. With known distances, we examine the various maximum magnitude-rate of decline relationships that have been established for classical novae. We find that these four objects show a similar level of scatter about these relationships as seen in larger samples of novae whose distances were determined using indirect techniques. We also examine the nebular expansion parallax method and find that it fails for three of the four objects. In each case it was possible to find an explanation for the failure of that technique to give precise distance estimates. DQ Her appears to suffer from an anomalously high extinction when compared to field stars on its sight line. We suggest that this is likely due to local material, which may also be the source of the IRAS detections of this object.NASA from the Space Telescope Science Institute AR12617NASA NAS 5-26555McDonald Observator
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The Internal Proper Motions Of Stars In The Open Cluster M35
Relative proper motions, based on 108 orbits of Hubble Space Telescope Fine Guidance Sensor data extending from 1992 to 2006, are reported for 74 stars in the open cluster M35 (NGC 2168). A subset of 22 of these objects are then used to compute the cluster's internal proper motion dispersions in both right ascension and declination. We find that these dispersions are equal to within their measurement errors. The average one-dimensional dispersion is 0.018 +/- 0.002 arcsec century(-1). When combined with the M35 radial velocity dispersion of 0.65 +/- 0.10 km s(-1) found by Geller et al., this produces a cluster distance of 762 +/- 145 pc. Using isochrone fits to the cluster main sequence, this distance suggests that M35 has an age of about 133 Myr. Although this age is consistent with that typically found for M35, the formal error in the dynamical distance of +/- 19% can accommodate ages between 65 Myr and 201 Myr.McDonald Observator
Detection of a Third Planet in the HD 74156 System Using the Hobby-Eberly Telescope
We report the discovery of a third planetary mass companion to the G0 star HD
74156. High precision radial velocity measurements made with the Hobby-Eberly
Telescope aided the detection of this object. The best fit triple Keplerian
model to all the available velocity data yields an orbital period of 347 days
and minimum mass of 0.4 M_Jup for the new planet. We determine revised orbital
periods of 51.7 and 2477 days, and minimum masses of 1.9 and 8.0 M_Jup
respectively for the previously known planets. Preliminary calculations
indicate that the derived orbits are stable, although all three planets have
significant orbital eccentricities (e = 0.64, 0.43, and 0.25). With our
detection, HD 74156 becomes the eighth normal star known to host three or more
planets. Further study of this system's dynamical characteristics will likely
give important insight to planet formation and evolutionary processes.Comment: 24 pages, 4 tables, 6 figures. Accepted for publication in ApJ. V2
fixed table 4 page overrun. V3 added reference
The Mass of the Candidate Exoplanet Companion to HD136118 from Hubble Space Telescope Astrometry and High-Precision Radial Velocities
We use Hubble Space Telescope Fine Guidance Sensor astrometry and
high-cadence radial velocities for HD136118 from the HET with archival data
from Lick to determine the complete set of orbital parameters for HD136118b. We
find an orbital inclination for the candidate exoplanet of i_{b} = 163.1 +- 3.0
deg. This establishes the actual mass of the object, M_{b} = 42^{+11}_{-18}
MJup, in contrast to the minimum mass determined from the radial velocity data
only, M_{b}sin{i} ~ 12 MJup. Therefore, the low-mass companion to HD 136118 is
now identified as a likely brown dwarf residing in the "brown dwarf desert".Comment: 35 pages, 12 figures, 10 tables. Accepted for publication in
Astrophysical Journa
The Hot R Coronae Borealis Star DY Centauri is a Binary
The remarkable hot R Coronae Borealis (RCB) star DY Cen is revealed to be the first and only binary system to be found among the RCB stars and their likely relatives, including the extreme helium stars and the hydrogen-deficient carbon stars. Radial velocity determinations from 1982 to 2010 have shown that DY Cen is a single-lined spectroscopic binary in an eccentric orbit with a period of 39.67 days. It is also one of the hottest and most H-rich member of the class of RCB stars. The system may have evolved from a common envelope to its current form.Spanish Ministry of Economy and Competitiveness AYA-2011-27754McDonald Observator
Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Selected Hyads
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 FGS 3, and newer data for 3 Hyads from
FGS 1R, both white-light interferometers on the Hubble Space Telescope (HST).
We obtain member parallaxes from six individual Fine Guidance Sensor (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 refer- ence 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) determina- tions, 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, = 47.5
pc, for the core a \pm 1 - {\sigma} dispersion depth of 3.6 pc, and a minimum
depth from individual components of 16.0 \pm 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 \pm 0.01, a value close to the previous Hipparcos values,
m-M=3.33\pm 0.02.Comment: 21 pages, 7 figures, Astronomical Journal, accepted 2011-3-
A Planetary Companion to gamma Cephei A
We report on the detection of a planetary companion in orbit around the
primary star of the binary system Cephei. High precision radial
velocity measurements using 4 independent data sets spanning the time interval
1981--2002 reveal long-lived residual radial velocity variations superimposed
on the binary orbit that are coherent in phase and amplitude with a period or
2.48 years (906 days) and a semi-amplitude of 27.5 m s. We performed a
careful analysis of our Ca II H & K S-index measurements, spectral line
bisectors, and {\it Hipparcos} photometry. We found no significant variations
in these quantities with the 906-d period. We also re-analyzed the Ca II
8662 {\AA} measurements of Walker et al. (1992) which showed possible
periodic variations with the ``planet'' period when first published. This
analysis shows that periodic Ca II equivalent width variations were only
present during 1986.5 -- 1992 and absent during 1981--1986.5. Furthermore, a
refined period for the Ca II 8662 {\AA} variations is 2.14 yrs,
significantly less than residual radial velocity period. The most likely
explanation of the residual radial velocity variations is a planetary mass
companion with sin = 1.7 and an orbital semi-major axis
of 2.13 AU. This supports the planet hypothesis for the residual
radial velocity variations for Cep first suggested by Walker et al.
(1992). With an estimated binary orbital period of 57 years Cep is the
shortest period binary system in which an extrasolar planet has been found.
This system may provide insights into the relationship between planetary and
binary star formation.Comment: 19 pages, 15 figures, accepted in Ap. J. Includes additional data and
improved orbital solutio
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