scholarly journals The HIPPARCOS parallax for Polaris

2013 ◽  
Vol 550 ◽  
pp. L3 ◽  
Author(s):  
F. van Leeuwen
Keyword(s):  
Hipparcos Parallax

scholarly journals Hipparcos Positions of B/Be Stars on the HR Diagram

2000 ◽  
Vol 175 ◽  
pp. 117-128 ◽  
Author(s):  
Danielle Briot ◽  
Noel Robichon
Keyword(s):  
Spectral Type ◽  
Rotational Velocity ◽  
Absolute Magnitude ◽  
Be Stars ◽  
Class V ◽  
B Stars ◽  
Luminosity Class ◽  
The Mean ◽  
Absolute Magnitudes ◽  
Hipparcos Parallax

AbstractAbsolute magnitudes of Be and B stars are computed for each spectral type and luminosity class V and IV, using the Hipparcos parallax measurements. Some simulations have been carried out in order to estimate the effects which could bias the mean absolute magnitude calculations. As a result, only stars with σπ/π < 15% have been used. A first result is that B stars are fainter than previous estimations by about 0.5 magnitude on average. We then observe that on average Be stars are brighter than B stars of the same spectral type and this over-luminosity increases with the spectral type. A possible interpretation is proposed based on the fact that the rotational velocity of the late Be stars is near the critical rotational velocity.

scholarly journals Two Aspects of Using Hipparcos Data for Studying Multiperiodic Stellar Pulsations

2000 ◽  
Vol 176 ◽  
pp. 46-49
Author(s):  
M. Jerzykiewicz
Keyword(s):  
Effective Temperature ◽  
Hydrogen Burning ◽  
Stellar Pulsations ◽  
Scuti Star ◽  
Frequency Ratios ◽  
Hipparcos Parallax ◽  
Multicolor Photometry ◽  
Hr Diagram

AbstractTwo aspects of using Hipparcos data for studying multiperiodic stellar pulsations involve (1) deriving frequencies of multiperiodic pulsators from Hipparcos Epoch Photometry, and (2) using Hipparcos parallaxes together with other data, such as the frequencies, frequency ratios and multicolor photometry, to identify pulsation modes. Details are examined by looking at the δ Scuti star DK Virginis. From Hipparcos Epoch Photometry, two frequencies are derived. These frequencies are then verified by showing that they also fit all available ground-based observations of the star. In addition, Hipparcos parallax and a photometric effective temperature are used to compare the position of DK Vir in the HR diagram with evolutionary tracks. The star turns out to be at the end of core-hydrogen-burning stage of its evolution or slightly beyond, with a mass of 2.2 M⊙, or somewhat smaller. The observed frequencies indicate that the two detected modes are p3 and p2, while the relatively large photometric amplitudes imply ℓ ≲ 2.

Radial Velocities Without Spectroscopy

1999 ◽  
Vol 170 ◽  
pp. 77-81 ◽  
Author(s):  
Søren Madsen ◽  
Lennart Lindegren ◽  
Dainis Dravins
Keyword(s):  
Radial Velocity ◽  
Proper Motion ◽  
Open Clusters ◽  
Radial Velocities ◽  
Motion Data ◽  
Hipparcos Parallax

AbstractWe discuss non-spectroscopic (astrometric) ways to determine radial velocities and their potentials in future astrometric missions. Radial-velocity accuracies are presented, based on Hipparcos parallax and proper motion data for several open clusters.

scholarly journals Systematic biases and uncertainties of Hipparcos parallax

2007 ◽  
Vol 3 (S248) ◽  
pp. 78-81
Author(s):  
X. P. Pan
Keyword(s):  
Strong Support ◽  
Lessons Learned ◽  
Error Sources ◽  
Lunar Occultation ◽  
Long Baseline ◽  
Future Space ◽  
Systematic Biases ◽  
Celestial Reference Frame ◽  
Radio Stars ◽  
Hipparcos Parallax

AbstractGround-based optical/IR interferometers have provided strong support to the space-based astrometric mission Hipparcos ever since the Hipparcos instrument was in operation in 1989. Interferometric observations also produced critical corrections of orbital motion to many targets, including radio stars, which link the Hipparcos system to the International Celestial Reference Frame (ICRF). In particular, orbital parallax from interferometers confirmed the 10% bias of the Pleiades distance from Hipparcos, and thus avoids revision of classical astronomy. Significant offsets and errors of Hipparcos parallax introduced by binary jitters are demonstrated in this work. By comparing the Hipparcos results with long baseline interferometry and other techniques including spectroscopy, multi-color photometry, Main-Sequence fitting, light curve measurements, Lunar occultation, Fine Guidance Sensor, etc., systematic biases and uncertainties of Hipparcos parallaxes are investigated and analyzed. We have established good models for major error sources of Hipparcos parallax, such as zonal bias, binary jitters, and luminosity-dependent errors. The lessons learned from the systematic biases of Hipparcos parallax are valuable to future space missions like SIM and Gaia.

scholarly journals Suggestion to Revise the Hipparcos-Parallax of Cepheids Belonging to Binary Systems

1998 ◽  
Vol 11 (1) ◽  
pp. 580-580
Author(s):  
L. Szabados
Keyword(s):  
Adverse Effect ◽  
Binary Systems ◽  
Spectroscopic Studies ◽  
Distance Scale ◽  
Major Error ◽  
Error Source ◽  
Orbital Elements ◽  
The Future ◽  
Hipparcos Parallax

It has been suspected (Szabados 1997) that the apparent orbit of previously unresolved binaries involving a Cepheid component falsifies the Hipparcos-parallaxes deduced for these Cepheids. Since the incidence of binaries among Cepheids exceeds 50 per cent, this adverse effect on the parallax determination is a major error source. An obvious remedy is to repeat the determination of the five astrometric parameters for the Cepheids, members in binary systems, taking into accountthe orbital elements known from spectroscopic studies. This will result in more precise parallaxes and cosmic distance scale. Moreover, these Cepheidsare ideal targets for the future microarcsec astrometric missions. This study was partly supported by OTKA-grants T 014852 and T 022946.

scholarly journals The Luminosity Calibration of the HR Diagram

1998 ◽  
Vol 11 (1) ◽  
pp. 558-558
Author(s):  
A.E. Gómez ◽  
X. Luri ◽  
M.O. Mennessier ◽  
J. Torra ◽  
F. Figueras ◽  
...  
Keyword(s):  
Likelihood Estimation ◽  
Absolute Magnitude ◽  
Motion Data ◽  
Final Sample ◽  
Peculiar Stars ◽  
Absolute Magnitudes ◽  
The Individual ◽  
Available Information ◽  
Hipparcos Parallax ◽  
Hr Diagram

An extensive work on the luminosity calibration of the HR diagram has been performed using the LM method based on the Maximum Likelihood estimation (Luri et al. 1996). The method uses all available information: Hipparcos parallax and proper motion data as well as radial velocities and some measured spectroscopic or photometric parameters related to luminosity. On the other hand, the method takes into account the censorship of the sample and the errors of the data. Finally, it is able to identify and separate in a given sample, groups with different luminosity, kinematical or spatial characteristics providing not only the corresponding luminosity calibration relationship, but also improved individual absolute magnitude estimates. In order to asses how reliable the luminosity calibrations based on the MK spectral classification are, the LM method has been applied to a sample of B to K stars with MK classification selected from the Hipparcos survey. All known binaries, variables and spectroscopically peculiar stars were removed from the sample. The final sample contains 22054 stars. Our results show that the relation between absolute magnitude and luminosity class has a large intrinsic dispersion. As a consequence, the assignation to a star of a mean absolute magnitude given by a MK classification calibration is a rough procedure. It is preferable to use the individual absolute magnitudes estimated using all the available information for each star, like the estimates provided by the LM method (Gómez et al. 1997).

scholarly journals A METHOD FOR ESTIMATING PARALLAXES OF VCBS: MODIFICATION TO HIPPARCOS PARALLAX MEASUREMENTS

2013 ◽  
Vol 23 ◽  
pp. 64-73
Author(s):  
M. A. Al-WARDAT ◽  
A. TAANI ◽  
M. ASPLUND
Keyword(s):  
Energy Distribution ◽  
Binary Stars ◽  
Spectral Energy Distribution ◽  
Model Atmosphere ◽  
Atmospheric Modeling ◽  
Close Binary ◽  
Spectral Energy ◽  
Geometrical Parameters ◽  
The Masses ◽  
Hipparcos Parallax

We presented a method useful for estimating parallaxes of visually close binary stars (VCBS). The method depends on atmospheric modeling of the components of the VCBS. We construct model atmospheres by using a grid of Kurucz solar metalicity blanketed models1, which can be applied to calculate the synthetic spectral energy distribution for each component of the binary separately. In addition to study the entire system. However, the entire observational spectral energy distribution of the system was used as a reference for the comparison with the synthetic ones. We choose Hip4809 system to investigate the method, and we also study its physical and geometrical parameters. The new parallax of the system was estimated as π = 40.32 ± 5.00 mas, which disagrees with the Hipparcos parallax measurement (13.94 ± 0.90 mas). Furthermore the model atmosphere parameters of the components of the system were derived as: [Formula: see text], [Formula: see text], log ga = 4.50 ± 0.13, log gb = 4.50 ± 0.13, Ra = 0.94 ± 0.12R⊙, Rb = 0.93 ± 0.12R⊙, Depending on the derived parameters, the masses of the system's components were estimated as 1.03 ± 0.02M⊙ and 1.01 ± 0.02M⊙ for the primary and secondary components respectively, and their spectral types were concluded as G6V for both of them.

scholarly journals Globular Cluster Ages from Hipparcos Subdwarfs

1999 ◽  
Vol 183 ◽  
pp. 69-69
Author(s):  
F. Pont ◽  
D.A. Vandenberg ◽  
M. Mayor ◽  
C. Turon
Keyword(s):  
Stellar Evolution ◽  
Globular Clusters ◽  
Direct Sequence ◽  
Reliable Determination ◽  
Upper Limit ◽  
Minimum Age ◽  
The Difference ◽  
The Universe ◽  
Hipparcos Parallax

The new Hipparcos parallax data for local subdwarfs allow a much more reliable determination of the distance to globular clusters (by direct sequence fitting) than was previously possible. Earlier studies (Reid 1997, Gratton et al. 1997) have reported larger distances than expected, especially for the most metal-poor clusters, implying much younger ages. In our study of Hipparcos subdwarfs applied to M92 — representative of the oldest, most metal-poor clusters — we find however a distance only slightly in excess of previous expectations. We show, using Monte Carlo simulations, that most of the difference may be explained by our more detailed treatment of the Lutz-Kelker and selection biases. With up-to-date stellar evolution models, we derive a minimum age of 13 Gyr for the Universe. This value, although lower than previous estimates, still imposes a rather strict upper limit to Ho in the context of standard cosmological models.

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