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J/AJ/110/1229 ROSAT X-ray survey in NGC 6475 (Prosser+ 1995)
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An X-ray survey of the open cluster NGC 6475 (M7) with ROSAT.
Prosser C.F., Stauffer J.R., Caillault J.-P., Balachandran S.,
Stern R.A., Randich S.
<Astron. J. 110, 1229 (1995)>
=1995AJ....110.1229P
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ADC_Keywords: Clusters, open ; X-ray sources ; Photometry, CCD
Mission_Name: ROSAT
Abstract:
A ROSAT X-ray survey, with complementary optical photometry, of the
open cluster NGC 6475 has enabled the detection of ~50 late-F to K0
and ~70 K/M dwarf new candidate members, providing the first reliable
detection of low-mass stars in this low galactic latitude, 220Myr old
cluster. The X-ray observations reported here have a typical limiting
sensitivity of L_X_ ~ 10^29^erg/s. The detection frequency of early
type cluster members is consistent with the hypothesis that the X-ray
emitting early type stars are binary systems with an unseen, low-mass
secondary producing the X-rays. The ratio between X-ray and bolometric
luminosity among NGC 6475 members saturates at a spectral-type/color
which is intermediate between that in much younger and in much older
clusters, consistent with rotational spindown of solar-type stars upon
their arrival on the ZAMS. The upper envelope of X-ray luminosity as a
function of spectral type is comparable to that of the Pleiades, with
the observed spread in X-ray luminosity among low-mass members being
likely due to the presence of binaries and relatively rapid rotators.
However, the list of X-ray selected candidate members is likely biased
against low-mass, slowly rotating single stars. While some preliminary
spectroscopic information is given in an appendix, further
spectroscopic observations of the new candidate members will aid in
interpreting the coronal activity among solar-type NGC 6475 members
and their relation to similar stars in older and younger open
clusters.
Objects:
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RA (2000) DE Designation(s)
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17 53.9 -34 49 NGC 6475 = M 7
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 129 178 X-ray source list
table5.dat 127 21 X-ray source list: Weaker possible sources
table8.dat 79 25 ESO CASPEC radial and rotational velocities
(1994 April 21-25 UT)
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Byte-by-byte Description of file: table4.dat table5.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID Identification number [PSC95]
5- 6 I2 h RAh Right ascension (2000)
8- 9 I2 min RAm Right ascension (2000)
11- 14 F4.1 s RAs Right ascension (2000)
16 A1 --- DE- Declination sign
17- 18 I2 deg DEd Declination (2000)
20- 21 I2 arcmin DEm Declination (2000)
23- 24 I2 arcsec DEs Declination (2000)
26- 29 F4.1 arcmin Off-axis Distance off-axis from the center of the
PSPC field
31- 35 I5 s Exp Exposition time
37- 42 F6.4 s-1 CRate Count rate
44- 49 F6.4 s-1 e_CRate rms uncertainty on CRate
51- 54 F4.1 --- S/Nb Broadband (0.07-2.4keV) signal to noise ratio
56- 59 F4.1 --- S/Nh Hardband (0.5-1.8keV) signal to noise ratio
61- 65 F5.2 [10-7W] logLx X-ray luminosity
67- 68 A2 --- l_HR [>= ] Limit flag on HR
69- 72 F4.1 --- HR ? Hardness ratio
74- 76 I3 arcsec DRA ? Offset on right ascension between X-ray and
optical positions
78- 80 I3 arcsec DDE ? Offset on declination between X-ray and
optical positions
82- 86 F5.2 mag Vmag ? V magnitude
88- 91 F4.2 mag B-V ? B-V colour index
93- 96 F4.2 mag V-Ic ? V-Ic colour index
98- 99 A2 --- Member [YN? ] Membership
101 I1 --- o_Vmag ? Number of observation in V band
102 I1 --- o_Bmag ? Number of observation in B band
103 I1 --- o_Icmag ? Number of observation in Ic band
105-108 A4 --- Name Optical counterpart name when available (1)
110-119 A10 --- GSC GSC number
121-140 A20 --- Note Notes (2)
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Note (1): Koelbloed (1959BAN....14..265K) name when available,
otherwise, a letter designation "A", "B", etc. is assigned.
Note (2): the following abbreviations are used:
?source: weak sources which have been considered questionable upon
visual inspection of the data
rib: sources which may be partially obscured by the PSPC
support structure
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Star Star name
8- 12 F5.2 mag Vmag V Magnitude
14- 17 F4.2 mag B-V B-V colour index
19- 22 F4.2 mag V-Ic V-Ic colour index
24- 26 I3 km/s RV Radial velocity
27 A1 --- u_RV Uncertainty flag (:) on RV
29- 30 A2 --- l_Vrot [<= ] Limit flag on Vrot
31- 32 I2 km/s Vrot ? Rotational velocity
33 A1 --- u_Vrot Uncertainty flag on Vrot
35- 36 A2 --- Member [YN? ] Member
38- 50 F13.5 d HJD Heliocentric Julian date
52- 79 A28 --- Note Notes
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History: Prepared via OCR at CDS.
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(End) James Marcout, Patricia Bauer [CDS] 13-Jun-1997