Data Mining for Red Dwarf Stars in SDSS

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Red dwarfs are by far the most common but also the most inconspicuous type of star. They are cool, small (7% to 60% of solar mass), main sequence stars found towards the lower right hand corner of the Hertzsprung-Russell diagram.

Some red dwarfs are flare stars with frequent eruptions that greatly increase their brightness for a short time. These flares only take a few minutes to reach maximum brightness and flare stars erupt at irregular intervals with flares spaced anything between an hour and a few days apart.

Techniques have been developed to identify red dwarf in the Sloan Digital Sky Survey (SDSS). The table below is extracted from the article "Updated colors for cool stars in the SDSS".

Extracting red dwarfs from the SDSS archives

The CasJobs facility can be used to search for specific classes of astronomical objects within the SDSS database. The script shown below demonstrates how this can be done. The key features of the SQL script are as follows:-

1. The number of objects to be selected.
2. The characteristics of the selected objects that will be reported to the user.
3. Constraints on the objects to be selected based on these chosen characteristics.

In this example I required all five bands of magnitude data for a maximum of 65,000 stars with 11 constraints applied to the star chosen. The first 5 constraints exclud very faint stars, the next 4 excluded stars that previous trials had shown to have photometric errors and/or not to be red dwarfs and the final 2 made use of the published chart, as shown above, to select a sub-type of red dwarf centered around spectral type M2. The script can, of course, be modified to suit what the user requires but I find it convenient to limit the output to 65,000 stars so that subsequent data manipulation using Excel is simplified.

Confirming the status of the red dwarfs

The SQL script generated a total of 27,435 hits. Each of these was analysed using the predictive equations shown above.

It is possible to use the published data on SDSS red dwarfs to determine many of the key characteristics of the individual stars. This was well explained in an article by Edgardo Rubén Masa Martín published in the Journal of Double Star Observations.

Very late M dwarfs in SDSS (M8.0 to M9.5)

Details of the late M dwarfs discovered using the same technique as described above but with (r-i) > 2.01.

Other useful links

The Solar Neighbourhood Series

Photometric Distance Estimate

Martin Nicholson - Daventry, United Kingdom.

This page was last updated on July 2nd 2010.