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ORIONXSTAR: Help

ORIONXSTAR - ROSAT HRI Orion Group 1 Stars


Overview

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 10^21 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

1995ApJ...445..280G

References

Gagne, M., Caillault, J.-P., and Stauffer, J.R. 1995, ApJ, 445, 280.

Provenence

This database was created at the HEASARC in August 1998 based on a computer-readable version of Table 6 of Gagne et al. (1995) that was obtained from the CDS (their catalog J/ApJ/445/280).

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.


Contact Person

Questions regarding the ORIONXSTAR database table can be addressed to the HEASARC User Hotline.
If you have any problems, please consult the help page or mail ledas-help@star.le.ac.uk
 
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