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J/AJ/110/1229        ROSAT X-ray survey in NGC 6475 (Prosser+ 1995)

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
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 LX ∼ 1029erg/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: ---------------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------------- 17 53.9 -34 49 NGC 6475 = M 7 ---------------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table4 140 178 X-ray source list table5 140 21 X-ray source list: Weaker possible sources table8 79 25 ESO CASPEC radial and rotational velocities (1994 April 21-25 UT)
Byte-by-byte Description of file: table4 table5
Bytes Format Units Label Explanations
1- 3 I3 --- ID Identification number [PSC95] 5- 6 I2 h RAh Right ascension (J2000) 8- 9 I2 min RAm Right ascension (J2000) 11- 14 F4.1 s RAs Right ascension (J2000) 16 A1 --- DE- Declination sign 17- 18 I2 deg DEd Declination (J2000) 20- 21 I2 arcmin DEm Declination (J2000) 23- 24 I2 arcsec DEs Declination (J2000) 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)
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
Byte-by-byte Description of file: table8
Bytes Format Units Label Explanations
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
History: Prepared via OCR at CDS.
(End) James Marcout, Patricia Bauer [CDS] 13-Jun-1997
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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