J/A+A/402/571 X-ray study of NGC 2451 A and B. (Huensch+ 2003)
An X-ray study of the open clusters NGC 2451 A and B.
Huensch M., Weidner C., Schmitt J.H.M.M.
<Astron. Astrophys., 402, 571-586 (2003)>
=2003A&A...402..571H 2003A&A...402..571H
ADC_Keywords: Clusters, open ; X-ray sources
Keywords: stars: activity - stars: coronae - X-rays: stars -
Hertzsprung-Russell (HR) and C-M diagrams -
open clusters and associations: individual: NGC 2451
Abstract:
We have conducted a detailed study of the object NGC 2451, which
actually consists of two different open clusters A and B along the
same line of sight at 206pc and 370pc distance, respectively. Although
belonging to the nearest clusters, they have not been much
investigated until present due to strong contamination by field stars.
ROSAT X-ray observations and optical UBVR photometry are used to
identify cluster members by means of X-ray emission and
colour-magnitude diagrams. The identified stars concentrate nicely
around the expected main sequences in the colour-magnitude diagram at
the distances derived from astrometric investigations. Altogether, 39
stars are identified as member candidates of the nearer cluster A, 49
stars as member candidates of the more distant cluster B, and 22 faint
stars are probably members of either of the two clusters, but due to
large errors it is not clear to which one they belong. Further 40
stars identified with X-ray sources are probably non-members. For the
first time, the range of known probable cluster members of NGC 2451 A
and B has been extended downwards the main sequence to stars of
spectral class M. Isochrone fitting yields an age of 50 to 80Myrs for
NGC 2451 A and ≃50Myrs for NGC 2451 B, consistent with the X-ray
luminosity distribution functions, which are comparable to other
clusters in the same age range. Except from the occurence of four
flares, the stars of both clusters do not show strong long-term X-ray
variability exceeding a factor 5 over a time span of 1 to 3 years.
Description:
The ROSAT X-ray observations were carried out at three different
epochs between 1992 and 1996. Two PSPC (called "A" and "B") and one
HRI ("H") observations were scheduled on NGC 2451.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
x-obs.dat 46 324 Detected X-ray sources (tables 3-6 of paper)
sources.dat 102 150 Final list of X-ray sources identified with stars
(tables 7-10 of paper)
notes.dat 74 10 Individual notes
tables.tex 96 691 LaTeX version of the tables
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See also:
J/A+A/341/469 : Geneva photometry of NGC 2451 and HR 2968 (Carrier+ 1999)
Byte-by-byte Description of file: x-obs.dat
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Bytes Format Units Label Explanations
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1 A1 --- Obs [ABCH] Detection location (1)
3- 5 I3 --- Xno X-ray source number
7- 13 F7.5 ct/s CR X-ray count rate
16- 22 F7.5 ct/s e_CR Mean error on CR
25- 30 F6.3 --- HR ? Hardness ratio
33- 37 F5.3 10-16W/m2 Xflux X-ray flux (in 10-13erg/cm2/s)
39- 43 F5.3 10+23W Xlum ? X-ray luminosity (2)
45- 46 A2 --- eDet [h s UV] source is detected in the soft (s),
hard (h) passband only, and also in UV
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Note (1): Observation where the source is detected
A = PSPC pointing A (table 3)
B = PSPC pointing B (table 4)
C = PSPC pointing C (table 5)
H = HRI pointing (table 6)
Note (2): the luminosity is given only if the distance is known, i.e.
when it is a probable cluster member.
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Byte-by-byte Description of file: sources.dat
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Bytes Format Units Label Explanations
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1 A1 --- Mem [ABnm] Member of NGC 2451A (A) or
NGC 2451B (B), m=member n=non-member
2- 4 I3 --- Xno X-ray source number
6- 8 I3 --- Wno ? Williams number
9 A1 --- m_Wno Multiplicity index on Wno
10- 11 I2 h RAh Right Ascension J2000 (hours)
13- 14 I2 min RAm Right Ascension J2000 (minutes)
16- 17 I2 s RAs Right Ascension J2000 (seconds)
20 A1 --- DE- Declination J2000 (sign)
21- 22 I2 deg DEd Declination J2000 (degrees)
24- 25 I2 arcmin DEm Declination J2000 (minutes)
27- 28 I2 arcsec DEs Declination J2000 (seconds)
30- 31 I2 arcsec Off Offset between X-ray and optical positions
33- 37 F5.2 mag Vmag V magnitude
38 A1 --- f_Vmag [*] *: value from the literature (2)
40- 44 F5.2 mag B-V B-V color index
45 A1 --- f_B-V [*] *: value from the literature (2)
47- 51 F5.2 mag (B-V)0 De-reddened color index
54 A1 --- Var [X] X: significant variations in the
X-ray flux
56- 60 F5.2 [10+23W] log(LX) ? X-ray luminosity
63- 67 F5.2 [---] log(LX/Lbol) ? Fraction of luminosity in X-ray
70- 78 A9 --- Sp Spectral type, in parentheses when derived
from color index
82- 95 A14 --- OptID Optical identification
96 A1 --- n_Xno [*] indicates a note detailed in notes.dat
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Note (2): value taken from the literature for bright stars
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Byte-by-byte Description of file: notes.dat
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Bytes Format Units Label Explanations
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1 A1 --- Obs Detection location, as in file x-obs.dat
2- 4 I3 --- Xno X-ray source number
6- 80 A75 --- Note text of the note
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History:
From electronic version of the journal
References:
Williams, 1966MNSSA..25..122W 1966MNSSA..25..122W
Williams, 1967MNSSA..26...30W 1967MNSSA..26...30W
Williams, 1967MNSSA..26..139W 1967MNSSA..26..139W
(End) Francois Ochsenbein [CDS] 26-Aug-2003