We present 348 X-ray emitting stars identified from correlating the Extended Chandra Multiwavelength Project ( ChaMP ) , a wide-area serendipitous survey based on archival X-ray images , with the Sloan Digital Sky Survey ( SDSS ) .
We use morphological star/galaxy separation , matching to an SDSS quasar catalog , an optical color-magnitude cut , and X-ray data quality tests to create our catalog , the ChaMP Extended Stellar Survey ( ChESS ) , from a sample of 2121 matched ChaMP/SDSS sources .
Our cuts retain 92 \% of the spectroscopically confirmed stars in the original sample while excluding 99.6 \% of the 684 spectroscopically confirmed extragalactic sources .
Fewer than 3 \% of the sources in our final catalog are previously identified stellar X-ray emitters .
For 42 catalog members , spectroscopic classifications are available in the literature .
We present new spectral classifications and H \alpha measurements for an additional 79 stars .
The catalog is dominated by main sequence stars ; we estimate the fraction of giants in ChESS is \sim 10 \% .
We identify seven giant stars ( including a possible Cepheid and an RR Lyrae star ) as ChAMP sources , as well as three cataclysmic variables .
We derive distances from \sim 10 - 2000 pc for the stars in our catalog using photometric parallax relations appropriate for dwarfs on the main sequence and calculate their X-ray and bolometric luminosities .
These stars lie in a unique space in the L _ { X } –distance plane , filling the gap between the nearby stars identified as counterparts to sources in the ROSAT All-Sky Survey and the more distant stars detected in deep Chandra and XMM-Newton surveys .
For 36 newly identified X-ray emitting M stars we calculate L _ { H \alpha } /L _ { bol } .
L _ { H \alpha } /L _ { bol } and L _ { X } /L _ { bol } are linearly related below L _ { X } /L _ { bol } \sim 3 \times 10 ^ { -4 } , while L _ { H \alpha } /L _ { bol } appears to turn over at larger L _ { X } /L _ { bol } values .
Stars with reliable SDSS photometry have an \sim 0.1 mag blue excess in u - g , likely due to increased chromospheric continuum emission .
Photometric metallicity estimates suggest that the sample is evenly split between the young and old disk populations of the Galaxy ; the lowest activity sources belong to the old disk population , a clear signature of the decay of magnetic activity with age .
Future papers will present analyses of source variability and comparisons of this catalog to models of stellar activity in the Galactic disk .