ORIONXST ivo://nasa.heasarc/orionxstar NASA/GSFC HEASARC Gagne, Caillault, Stauffer 2026-04-03 NASA/GSFC HEASARC help desk heasarc-vo at athena.gsfc.nasa.gov Star This catalog presents some of the results from 3 deep ROSAT High Resolution Imager (HRI) observations of the Orion Nebula star-forming region. The fields covered by the X-ray images contain over 1500 catalogued stars in a roughly 0.8 square degree region centered on the Trapezium. In all, 389 distinct X-ray sources were detected, at least two-thirds of which were associated with a single proper-motion cluster member. X-ray emission was detected from stars of all spectral types, from the massive O- and B-type components of the Trapezium to the coolest, low-mass pre-main-sequence (PMS) stars. In the research paper in which these data were presented (Gagne et al. 1995), the authors focussed primarily on X-ray emission from the late-type PMS stars. Of the ~100 late-type cluster members with measured spectral types, approximately three-fourths were detected; the authors derived X-ray luminosity upper limits for the remaining stars. They found that coronal X-ray emission appeared to turn on at around a spectral type of F6, with the upper envelope of activity increasing with decreasing effective temperature. The current database is a representation of Table 6 from Gagne et al. (1995) (notice that the data given in Tables 2 and 3 of this reference is included in the HEASARC database ORIONXRAY, q.v.) which lists X-ray and other data for 175 Orion stars for which spectral types, spectroscopic rotational velocities, and/or spot-modulated photometric rotational periods are available. The X-ray data (either detections or upper limits) are given in the form of X-ray luminosities log Lx and X-ray to bolometric luminosity ratios (log Lx/Lbol). The conversion factor from HRI counts to log Lx was derived for each star based on (i) an assumed 1 keV Raymond and Smith thermal spectrum, (ii) a distance of 440 pc, and (iii) a column density of 2 x 10<sup>21</sup> cm<sup>-2</sup> per magnitude of visual extinction A(V), where accurate A(V) values are used when available, or otherwise a moderate absorption of 0.25 magnitudes is assumed. Notice that, for stars not identified as candidate optical counterparts in Tables 2 and 3 of Gagne et al. (the HEASARC database ORIONXRAY), the derived upper limit to the X-ray luminosity usually corresponds to the 3 sigma upper limit to the observed count rate. For a handful of stars in the Trapezium region where a star was eliminated as a candidate optical counterpart, despite being within the source search circle, because a more likely counterpart had a smaller position offset, the upper limit corresponds to either half the observed X-ray source count rate or to 3 sigma, whichever is the highest. Such cases are indicated in this database by the presence of the string "NN" in the parameter 'Note'. This is a service provided by NASA HEASARC . 1995ApJ...445..280G https://heasarc.gsfc.nasa.gov/W3Browse/all/orionxstar.html Catalog Research served-by HEASARC TAP https://heasarc.gsfc.nasa.gov/xamin/vo/cone?showoffsets&table=orionxstar& GET text/xml 180 99999 true 83.5048481 -4.7436917 0.0166666666666667 https://heasarc.gsfc.nasa.gov/xamin/vo/tap https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/getvotable.pl?name=orionxstar GET text/xml https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3query.pl?tablehead=name=heasarc_orionxstar&Action=More+Options&Action=Parameter+Search&ConeAdd=1 STAR CATALOG 0.0166666666666667 X-ray public orionxstar ROSAT HRI Orion Group 1 Stars visual_ext Visual Extinction double nullable log_lxlbol_limit Limit Flag for log_lxlbol char nullable vmag V Magnitude phot.mag;em.opt.V double nullable bmag B Magnitude phot.mag;em.opt.B double nullable log_lx Log of X-ray Luminosity (in erg/s) log(erg/s) double nullable v_sin_i Projected Rotation Velocity (km/s) km/s short nullable dec Declination degree pos.eq.dec;meta.main double nullable "__x_ra_dec" System unit vector column double nullable v_sin_i_limit Limit Flag for v_sin_i char nullable "__row" System index column char nullable log_t_eff_flag Uncertainty Flag for log_t_eff char nullable visual_ext_flag Indicates When A(V) of 0.25 Magnitudes Is Assumed char nullable note Notes char nullable bii Galactic Latitude degree pos.galactic.lat double nullable log_lxlbol_flag Uncertainty Flag for log_lxlbol char nullable icmag Cousins System Ic Magnitude double nullable lii Galactic Longitude degree pos.galactic.lon double nullable "__y_ra_dec" System unit vector column double nullable class Browse Object Classification src.class short nullable ra Right Ascension degree pos.eq.ra;meta.main double nullable log_lx_limit Limit Flag on log_lx char nullable rotation_period Rotational Period (days) d double nullable name Object Designation meta.id;meta.main char nullable xray_number X-ray Number short nullable "__z_ra_dec" System unit vector column double nullable log_lxlbol Log of Ratio of X-ray to Bolometric Luminosity double nullable spect_type Spectral Type src.spType char nullable log_t_eff Log of Effective Temperature (in K) log(K) double nullable