ScienceProblem: ActiveStarProperMotions

PrimaryActor

Astronomer

---

ScienceGoal

To investigate the properties of nearby active stars e.g. dMes (red dwarves), including proper motions possibly indicating the presence of low-mass companions.

---

DataSets

Hipparcos, GCVS and other stellar catalogues of positions and spectra. Radio, x-ray and other surveys and any observations covering the required positions.

---

ProblemDescription:

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 (ICRS).

---

CurrentSolution:

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.

---

VOSolution:

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 be required.

---

KeyReferences:

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

---

---

GoodStyle: Please add comments below. This area should be used for refinement of the above document. If you want to ask questions or start a dialogue with the author, please use (or create) a topic in the Science Problems Forum. For other ScienceProblems, refer to the ScienceProblemList.
Author: Once the refinements here and comments in the forum die down, perhaps you could rewrite the problem, incorporating the comments and refinements.

---

Which specific data sets are likely to be held by AstroGrid

-- NicholasWalton - 17 Apr 2002

---

-- AnitaRichards - 06 Feb 2002