by Miloslav Druckmuller
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The Milky Way, Comet McNaught and the Magellanic Clouds by Miloslav Druckmuller |
The Magellanic Stream |
The Magellanic Clouds
I am doing a Ph.D. in Astronomy at the University of Virginia under the advisement of Steven R. Majewski. My thesis topic is "The Dynamical History of the Magellanic Clouds". I am studying the structure of the HI Magellanic Stream using radio data, and the stellar halos of the Magellanic Clouds using optical data mainly from the CTIO Blanco 4-meter and the Magellan 6.5-meter telescopes in Chile.
Radial Velocities
For the last two years I've been working on deriving barycentric radial velocities (sometimes referred to as "absolute" radial velocities) for the stars observed by the California & Carnegie Planet Search Project. About 1200 F-M type stars are being observed at Keck, Lick or the AAT (Anglo-Australian Telescope). Sofar I have obtained barycentric radial velocities for 889 stars. From comparison with standard stars (Udry et al. 1999a) the precision of the velocities is 35 m/s. The accuracy is typically ~0.3 km/s. I worked on this project with Debra Fischer from Fall 1999 - Summer 2000 and since then with Geoff Marcy.
My research is described in more detail in the abstract below. This paper has been accepted for publication in the August 2002 edition of ApJS (Astrophysical Journal Supplement). You can download the paper in either the postscript or pdf formats (see below). The four tables are also available in ASCII format (see below).
| Title: | Radial Velocities for 889 Late-type Stars | |
| Authors: | Nidever, David L., Marcy, Geoffrey W., Butler, R. Paul, Fischer, Debra A., and Vogt, Steven S. |
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We report radial velocities for 844 FGKM-type main sequence stars
and 45 K giants, most of which had either low-precision velocity
measurements or none at all. These velocities differ from the standard
stars of Udry et al. (1999a) by 0.035 km s-1
(RMS) for the 26 FGK standard
stars in commmon. The zero-point of our velocities differs from that of
Udry et al.: <V
present – VUdry
> = +0.053 km s-1.
Thus these new velocities agree with the best known standard stars both in precision
and zero-point, to well within 0.1 km s-1. Nonetheless, both these velocities and the standards suffer from three sources of systematic error, namely, convective blueshift, gravitational redshift, and spectral type mismatch of the reference spectrum. These systematic errors are here forced to zero for G2V stars by using the Sun as reference, with Vesta and day sky as proxies. But for spectral types departing from solar, the systematic errors reach 0.3 km s -1 in the F and K stars and 0.4 km s-1 in M dwarfs. Multiple spectra were obtained for all 889 stars during four years, and 782 of them exhibit velocity scatter less than 0.1 km s-1 . These stars may serve as radial velocity standards if they remain constant in velocity. We found 11 new spectroscopic binaries and report orbital parameters for them. |
Download the Paper:
nidever.pdf
Adobe Acrobat Version (780 KB)
nidever.ps
Postscript Version (1.5 MB)
This paper is also available from the astro-ph preprint server.
Download the Tables:
Table 1
Table 2
Table 3
Table 4
alpha Cen A&B
Dimitri Pourbaix has been doing research on the masses of alpha Cen A&B for some years now. I recently computed barycentric radial velocities of these stars for him which has allowed a more accurate calculation of their orbits and masses.
The research is described further in the abstract below. This paper has been accepted for publication in A&A (Astronomy & Astrophysics). You can download the paper in the pdf format.
| Title: | Constraining the difference of convective blueshift between the components of alpha Cen with precise radial velocities | |
| Authors: | Pourbaix, D., Nidever, D., McCarthy, C., Butler, R. P., Tinney, C. G., Marcy, G. W., Jones, H. R. A., Penny, A. J., Carther, B. D., Bouchy, F., Pepe, F., Hearnshaw, J. B., Skuljan, J., Ramm, D., and Kent, D. |
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New radial velocities of alpha Cen A&B obtained in the framework the
Anglo-Australian Planet Search Programme as well as in the CORALIE
programme are added to those by Endl et al.(2001) to improve the
precision of the orbital parameters. The resulting masses are 1.105
± 0.0070 M and 0.934 ± 0.0061
M for A and B respectively. The factors
limiting how accurately these masses can be derived from a combined
visual-spectroscopic solution are investigated. The total effect of the
convective blueshift and the gravitational redshift is also investigated
and estimated to differ by ~220 m/s between the components.
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Download the Paper:
pourbaix.pdf
Adobe Acrobat Version (127KB)
This paper is also available from the astro-ph preprint server.