scholarly journals Completing the Local Sample with Tycho

1998 ◽  
Vol 11 (1) ◽  
pp. 443-443
Author(s):  
R.L. Smart ◽  
R. Pannunzio ◽  
M.G. Lattanzi ◽  
B. Mclean

The Tycho Catalogue contains proper motions and low precision parallaxes with a median precisions of 25 mas, while having high precision B and V magnitudes (median precision of 0.07 and 0.06 respectivly). The number of highparallax stars is quite unexpected, with over 30 previously unreferenced, non-Hipparcos, stars with a parallax >500 mas and over 2000 with a parallax >250 mas. While many of these are probably mistakes, the completeness limit of Tycho and the precise magnitudes provide us with a way to intelligently build a complete picture of the nearby star field. Catalogues of nearby stars provide us with many fundamental parameters in the field of stellar astronomy, but the completness of known stars within say even 8pcs is still underestimated by about 30%, i.e., 50-60 systems (T.J. Henry, CSSS8, ASP Conf Series 64, 1994). In a new program at Torino we are using the Tycho Catalogue to intelligently build a list of possible candidates for a 1Opc volume. Figure 1 shows that Tycho will contain basically all ZAMS to spectral type M3 within 10 pes, M5 to 4pcs and M6 to 2pcs. A comparison of the photometric and Tycho distances provides a list free of giants and systems where binarity has affected the color. This list is then added to the Torino Parallax program where we expect to provide more precise parallaxes.

1986 ◽  
Vol 118 ◽  
pp. 247-249
Author(s):  
W. Gliese

At the General Assembly of the IAU at New Delhi van Altena reported on the new General Catalogue of Trigonometric Stellar Parallaxes (GCTSP) which was completed recently at the Yale Observatory. Time seems to be ripe now for the compilation of a Third Catalogue of Nearby Stars which will include all objects known to be nearer than 25 parsecs. This catalogue will contain positions, proper motions, radial velocities, spectral types, broad-band photometry, and parallaxes - quantities won by observations.


1978 ◽  
Vol 48 ◽  
pp. 523-526
Author(s):  
D. D. Polozhentsev ◽  
H. I. Potter

The reference photographic catalogue of the southern sky (RPC) will be a basis for investigations in the fields of astrometry, stellar astronomy, geodesy, space studies etc. in the southern hemisphere. It will be a catalogue of high precision, containing both bright and faint stars, reliably connected to the fundamental catalogue and giving an inertial coordinate system for a wide range of southern stars. The RPC will be an extension of the Goloseevo Plan (1) for the southern hemisphere. However, our project has its own peculiarities, mainly because there is no AGK3 type catalogue of the southern sky for the present epoch.


1998 ◽  
Vol 11 (1) ◽  
pp. 583-583
Author(s):  
S. Röser ◽  
U. Bastian ◽  
K.S. de Boer ◽  
E. Høg ◽  
E. Schilbach ◽  
...  

DIVA (Double Interferometer for Visual Astrometry) is a Fizeau interferometer on a small satellite. It will perform astrometric and photometric observations of at least 4 million stars. A launch in 2002 and a minimum mission length of 24 months are aimed at. A detailed description of the experiment can be obtained from the DIVA homepage at http://www.aip.de:8080/᷉dso/diva. An overview is given by Röser et al., 1997. The limiting magnitude of DIVA is about V = 15 for spectral types earlier than M0, but drops to about V = 17.5 for stars later than M5. Table 1 gives a short overview on DIVA’s performance. DIVA will carry out a skysurvey complete to V = 12.5. For the first time this survey will comprise precise photometry in at least 8 bands in the wavelength range from 400 to 1000 nm. DIVA will improve parallaxes by a factor of 3 compared to Hipparcos; proper motions by at least a factor of 2 and, in combination with the Hipparcos observations, by a factor of 10 for Hipparcos stars. At least 30 times asmany stars as Hipparcos will be observed, and doing this DIVA will fill the gap in observations between Hipparcos and GAIA. DIVA’s combined astrometric and photometric measurements of high precision will have important impacts on astronomy and astrophysics in the next decade.


2018 ◽  
Vol 620 ◽  
pp. A54 ◽  
Author(s):  
C. Saffe ◽  
M. Flores ◽  
P. Miquelarena ◽  
F. M. López ◽  
M. Jaque Arancibia ◽  
...  

Aims. In an effort to improve spectroscopic methods of stellar parameters determination, we implemented non-solar-scaled opacities in a simultaneous derivation of fundamental parameters and abundances. We wanted to compare the results with the usual solar-scaled method using a sample of solar-type and evolved stars. Methods. We carried out a high-precision determination of stellar parameters and abundances by applying non-solar-scaled opacities and model atmospheres. Our sample is composed of 20 stars, including main sequence and evolved objects. The stellar parameters were determined by imposing ionization and excitation equilibrium of Fe lines, with an updated version of the FUNDPAR program, together with plane-parallel ATLAS12 model atmospheres and the MOOG code. Opacities for an arbitrary composition and vmicro were calculated through the opacity sampling (OS) method. We used solar-scaled models in the first step, and then continued the process, but scaled to the abundance values found in the previous step (i.e. non-solar-scaled). The process finishes when the stellar parameters of one step are the same as in the previous step, i.e. we use a doubly iterated method. Results. We obtained a small difference in stellar parameters derived with non-solar-scaled opacities compared to classical solar-scaled models. The differences in Teff, log g, and [Fe/H] amount to 26 K, 0.05 dex, and 0.020 dex for the stars in our sample. These differences can be considered the first estimation of the error due to the use of classical solar-scaled opacities to derive stellar parameters with solar-type and evolved stars. We note that some chemical species could also show an individual variation greater than those of the [Fe/H] (up to ~0.03 dex) and varying from one species to another, obtaining a chemical pattern difference between the two methods. This means that condensation temperature Tc trends could also present a variation. We include an example showing that using non-solar-scaled opacities, the solution found with the classical solar-scaled method indeed cannot always verify the excitation and ionization balance conditions required for a model atmosphere. We discuss in the text the significance of the differences obtained when using solar-scaled versus non-solar-scaled methods. Conclusions. We consider that the use of the non-solar-scaled opacities is not mandatory in every statistical study with large samples of stars. However, for those high-precision works whose results depend on the mutual comparison of different chemical species (such as the analysis of condensation temperature Tc trends), we consider its application to be worthwhile. To date, this is probably one of the most precise spectroscopic methods for stellar parameter derivation.


2021 ◽  
pp. 89-98
Author(s):  
O. V. KIYAEVA ◽  
R. YA. ZHUCHKOV ◽  
I.S. IZMAILOV

There are high-precision positions, proper motions, parallaxes and radial velocities at the instant 2015.5 for all three components of the star ADS 48 ABF in the catalogue Gaia DR2 (2018). According to these data relative motions and the family of orbits were calculated by the Apparent Motion Parameters (AMP) method (Kiselev and Kiyaeva, 1980), and the best orbit was chosen for the inner pair AB. A perturbation with the period of 11 years was discovered according to Pulkovo observations of the outer pair. The reasons for the perturbation are discussed.


2017 ◽  
Vol 598 ◽  
pp. L7 ◽  
Author(s):  
P. Kervella ◽  
F. Thévenin ◽  
C. Lovis

Proxima and α Centauri AB have almost identical distances and proper motions with respect to the Sun. Although the probability of such similar parameters is, in principle, very low, the question as to whether they actually form a single gravitationally bound triple system has been open since the discovery of Proxima one century ago. Owing to HARPS high-precision absolute radial velocity measurements and the recent revision of the parameters of the α Cen pair, we show that Proxima and α Cen are gravitationally bound with a high degree of confidence. The orbital period of Proxima is ≈ 550 000 yr. With an eccentricity of 0.50+0.08-0.09, Proxima comes within 4.3+1.1-0.9 kau of α Cen at periastron, and is currently close to apastron (13.0+0.3-0.1 kau). This orbital motion may have influenced the formation or evolution of the recently discovered planet orbiting Proxima, as well as circumbinary planet formation around α Cen.


1949 ◽  
Vol 55 ◽  
pp. 16 ◽  
Author(s):  
P. van de Kamp ◽  
S. L. Lippincott
Keyword(s):  

1989 ◽  
Vol 8 ◽  
pp. 109-110
Author(s):  
Bruce Campbell

AbstractNine of 18 stars observed with a high precision radial velocity technique show long term, low level variations which imply the presence of companions in the range of 1 to 10 Jupiter masses. These companions could represent the tip of the planetary-mass spectrum.


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