To investigate the properties of nearby active stars e.g. dMes (red
dwarves), including proper motions possibly indicating the presence
of low-mass companions.
Hipparcos, GCVS and other stellar catalogues of positions and spectra.
Radio, x-ray and other surveys and any observations covering the
dMe and other active stars within a few 100 pc have fairly or very
good optical positions. They can have large proper motions and exhibit
erratic radio and high-energy flares. Some but not all are binary
stars. Some are used for geodetic (radio) VLBI and their positions
have been tracked with micro-arcsec accuracy. Such proper motion
studies could be used to measure wobbles due to sub-stellar
companions. However the radio emission can come from the stellar
surface, from its wind or from a binary wind interaction zone, and the
location can change as the activity state of the star changes. The
location of the radio emission can be correlated with binary orbital
phase, quiescence/outburst modes and optical stellar line changes
etc. but long-term monitoring - or data mining - is needed to
establish the pattern for each star.
Some objects are used to tie the optical and radio reference frames
Only a few objects have been studied in sufficient detail to track the
origin of radio with respect to optical emission, using dedicated
observations, for astrometric and geodetic purposes, often with
insufficient resources to analyse the stellar properties fully from
other perspectives. There are several hundred (possibly more)
candidate stars within reach of current/planned instruments.
Find the most accurate published optical positions and assessments of
proper motions. Locate all similar data (including serendipitous
inclusion in the footprints of observations of other targets) and use
to refine ephemerides. Find all radio, high-energy and optical
spectroscopy data (and eventually other data) at all epochs at the
correct positions (within the relevant instrumental and
ephemeris-related error boxes) and search for patterns to predict the
exact location of the radio emission with respect to the optical star,
based on optical, radio and high energy variability and spectra (and
stellar binary ephemerides if relevant). In some cases this may
reveal sub-stellar companions - as well as a great deal about the
physics of flares. In other cases follow-up monitoring with VLBI and
other instruments, using the appropriate identified diagnostics, may
Jones, D. L., Lestrade, J.-F., Preston, R. A., & Phillips, R. B. 1995, Astrophys. Space Sci., 223, 166 (1995) Searching for planets with VLBI.
Kovalevsky, J.+ 1997, Astron. Astrophys. 323, 620-633 The HIPPARCOS catalogue as a realisation of the extragalactic reference system
Lestrade, J.-F., Preston, R. A., Jones, D. L., Phillips, R. B., Rogers, A. E. E., Titus, M. A., Rioja, M. J., & Gabuzda, D. C. 1999, Astronomy and Astrophysics, v.344, p.1014-1026 (1999) High-precision VLBI astrometry of radio-emitting stars
Guirado, J. C.+ 1997, Astrophysical Journal v.490, p.835 Astrometric Detection of a Low-Mass Companion Orbiting the Star AB Doradus
Gunn, A. G., Hall, J. C., Lockwood, G. W., & Doyle, J. G. 1996, Astronomy and Astrophysics, v.305, p.146 Cross-correlation radial velocity measurements of chromospherically active binaries.
Lebach, D. E., Ratner, M. I., Shapiro, I. I., Ransom, R. R., Bietenholz, M. F., Bartel, N., & Lestrade, J.-F. 1999, The Astrophysical Journal, Volume 517, Issue 1, pp. L43-L46. Milliarcsecond Change of IM Pegasi Radio Position in 1 Hour Coincident with Sharp Rise in Flux Density
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Which specific data sets are likely to be held by AstroGrid
- 17 Apr 2002
- 06 Feb 2002