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 10^21 cm^(-2) 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'.
A: Position and proper-motion membership probability from McNamara et al. (1989) B: Position and proper-motion membership probability from Jones & Walker (1988) C: Position and proper-motion membership probability from van Altena et al. (1988) D: Proper-motion membership probability from McNamara & Huels (1983) E: Spectral type, V and Ic band photometry from Edwards et al. (1993) F: Spectral type from Strom (1993) G: Spectral type, B and V band photometry from Duncan (1993) H: Spectral type from Abt, Wang, & Cardona (1991) I: Spectral type from van Altena et al. (1988) J: Spectral type from the General Catalogue of Variable Stars (Kholopov et al. 1985) K: Spectral type from Walker (1983) L: Spectral type, B or V band photometry from Penston et al. (1975) or Penston (1973) M: Spectral type and V band photometry from Cohen & Kuhi (1979) N: Spectral type from Warren & Hesser (1977) O: Spectral type, B and V band photometry from Walker (1969) P: Spectral type from Parenago (1954) Q: V and I_c_ band photometry from Prosser et al. (1994) R: V and I_c_ band photometry from Attridge & Herbst (1992) S: Position or spectral type, V and I_c_ band photometry from Herbig & Terndrup (1986) T: B and V band photometry from Duncan (1993) U: B and V band photometry from McNamara et al. (1989) V: B and V band photometry from van Altena et al. (1988) W: B, V, and I_c_ band photometry from Rydgren & Vrba (1984) X: B and V band photometry from Warren & Hesser (1977) Y: I_c_ photographic magnitude from Jones & Walker (1988) Z: Position, B and V photographic magnitudes from Andrews (1981) AA: V photographic magnitude from Brun (1935) BB: Position, B photographic or V photovisual magnitude from Parenago (1954) CC: The bolometric luminosity of the late-type secondary cannot be determined DD: Rotational period from Attridge & Herbst (1994) EE: Rotational period from Attridge & Herbst (1992) FF: Rotational period from Mandel & Herbst (1991) GG: Rotational period from Walker (1990) HH: Spectroscopic rotational velocity from Strom (1993) II: Spectroscopic rotational velocity from Duncan (1993) JJ: Spectroscopic rotational velocity from Abt et al. (1991) KK: Spectroscopic rotational velocity from Walker (1990) LL: Spectroscopic rotational velocity from Hartmann et al. (1986) MM: One of two candidate optical counterparts. Upper limit corresponds to source flux NN: Possible blend. Upper limit corresponds to half of source flux
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