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Overview

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'.

Catalog Bibcode

References

Provenence

Parameters

Name
Source designation, P for Parenago, JW for Jones & Walker.

RA
The Right Ascension of the X-ray source.

Dec
The Declination of the X-ray source.

LII
The galactic longitude of the X-ray source.

BII
The galactic latitude of the X-ray source.

Xray_Number
X-ray number A running number used in Table 2 of the original reference that is ordered by increasing RA in J2000 co-ordinates.

Spect_Type
The spectral type of the star: a colon indicates an uncertain value.

Log_T_Eff
The logarithm of the effective temperature in degrees Kelvin (K).

Log_T_Eff_Flag
A flag for the effective temperature that is set to ":" if the value is considered uncertain.

Bmag
The Johnson B magnitude (either photometric or photographic).

Vmag
The Johnson V magnitude (either photometric or photographic).

Icmag
The Cousins Ic magnitude.

Visual_Ext
The visual extinction A(V) in magnitudes. When accurate absorption values are available from published estimates, photometric E(B-V) measurements, or the C_Hbeta_ extinction map of the nebula, they are listed in this column. Otherwise a moderate absorption (A(V) ~ 0.25mag) is assumed as indicated by the value of ")" in the parameter 'Visual_Ext_Flag'.

Visual_Ext_Flag
A flag that is set to ")" when A(V) of 0.25 magnitudes is assumed.

V_Sin_I_Limit
A flag for the parameter V_SIN_I that is set to "<" if the value is an upper limit.

V_Sin_I
The spectroscopic rotation velocity in km/s.

Rotation_Period
The rotational period in days.

Log_Lx_Limit
A flag for the parameter Log_Lx that is set to "<" if the value is an upper limit. The 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'.

Log_Lx
The logarithm of the X-ray luminosity in erg/sec.

Log_Lxlbol_Limit
A flag for the parameter Log_LxLbol (the ratio of the X-ray to the bolometric luminosity) that is set to "<" if the value is an upper limit. The 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'.

Log_Lxlbol
The ratio of the X-ray to the bolometric luminosity.

Log_Lxlbol_Flag
A flag for parameter Log_LxLbol (the ratio of the X-ray to the bolometric luminosity) that is set to ":" if the value is considered uncertain.

Note
Notes describing the sources of the optical data.

     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
  

Class
Browse classification, derived from the spectral type parameter.

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