J/ApJ/414/846 X-ray emission at the low-mass end (Barbera+ 1993)
X-ray emission at the low-mass end: results from an extensive
"Einstein Observatory" survey
Barbera M., Micela G., Sciortino S., Harden F.R. Jr, Rosner R.
<Astrophys. J. 414, 846 (1993)>
=1993ApJ...414..846B 1993ApJ...414..846B
ADC_Keywords: Stars, late-type ; X-ray sources
Keywords: stars: late-type - X-ray: stars
Mission_Name: Einstein
Abstract:
We have used all tha available data from the Einstein Observatory
Imaging Proportional Counter (IPC), and a critical compilation of
catalogued optical data, to measure the 0.16-3.5 keV X-ray emission
from 88 K and 169 M stars of luminosity classes IV, V and VI within
25 pc from the Sun. The IPC detected 54 out of the 88 K stars, 70
out of the 138 M stars with Mv less than 13.4 (corresponding
approximatively to M5), and 15 out of the 31 fainter M stars. We have
identified a subsample of surveyed stars that is statistically
representative of the population of K and M stars in the solar
neighborhood.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 104 257 Surveyed K and M stars
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Byte-per-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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2- 10 A9 --- Gliese Designation from Gliese (1969),
Gliese + Jahreiss (1979), cat. V/35,
or Wooley et al. (1970), cat. V/32
12- 13 I2 h RAh Right Ascension 1950 (hours)
15- 16 I2 min RAm Right Ascension 1950 (minutes)
18- 19 I2 s RAs [0/60] Right Ascension 1950 (seconds)
21 A1 - DE- Declination 1950 (sign)
22- 23 I2 deg DEd Declination 1950 (degrees)
25- 26 I2 arcmin DEm Declination 1950 (minutes)
28- 29 I2 arcsec DEs [0/60] Declination 1950 (seconds)
31- 35 F5.2 mag mv Apparent magnitude
37- 40 F4.2 mag B-V []? Colour index
42- 46 F5.2 mag Mv Absolute magnitude
48- 53 A6 -- Sp Spectral class
55- 58 F4.1 pc Distance of star
60- 63 I4 km/s U []? Velocity component
65- 68 I4 km/s V []? Velocity component
70- 73 I4 km/s W []? Velocity component
75 A1 --- AgeFlag [YOH] Y = young disk star,
O = old disk star,
H = halo population star.
77 A1 --- l_rate [<] Limit flag on rate
78- 82 F5.3 ct/s rate X-ray Count rate (see also column n_rate)
84- 88 F5.3 ct/s e_rate []? Mean error on rate
90 A1 --- l_log(Lx) [<] Limit flag on log(Lx)
91- 95 F5.2 [10-7W] log(Lx) X-ray flux in broad band (0.16-3.5keV)
97- 98 A2 --- n_rate [ML ] Method for count rate evaluation (1)
100 A1 --- Pflag [SP] Pointed flag:
S for stars observed serendipitously
P for pointed stars.
102-104 A3 --- Notes [vh,] Notes (2)
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Note (1): the methods are:
L = REV-1 Local method,
M = REV-1 Map method,
ML = Maximum Likelihood method
Note (2): the following symbols are used:
v = stars with evidence of long term X-ray variability according
to the Maximum Likelihood method adopted (Sciortino and Micela 1992),
h = stars observed also with the HRI on board the Einstein Observatory.
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Table 2: Distribution of K and M stars in Young disk (Y), Old disk (O),
Halo population (H), and stars with unknown space velocities (U)
for the optical sample (row 1), X-ray subsample made of the stars
with angular distance from the centre of any IPC field greater
than 3' (row 2), redefined X-ray serendipitous sample (row 3) and,
X-ray representative sample (row 4). The fractions of stars in
each age group are given in parenthesis.
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| K stars | M stars
Sample | Y O H U | Y O H U
-------------------------------------------------------------------------------
Optical |191(30%) 308(48%) 16(2%) 131(20%)|157(15%) 241(23%) 21(2%) 616(60%)
Offax > 3' | 21(44%) 18(37%) 1(2%) 8(17%)| 15(18%) 25(30%) 2(2%) 41(50%)
Serendipit.| 14(36%) 16(41%) 1(3%) 8(20%)| 14(20%) 17(24%) 2(3%) 38(53%)
Represent. | 23(35%) 33(50%) 2(3%) 8(12%)| 32(25%) 47(37%) 5(4%) 43(34%)
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Table 3: Results of the K-S test for the rejection of the hypothesis
that the distribution of Mv(mv) for the stars of the optical and
X-ray subsamples are extracted from the same parent population.
Three different subsamples are considered: the stars within the
entire volume of 25 pc radius, within 12 pc (only for the K stars)
and within 8 pc (only for the M stars).
-----------------------------------
K stars M stars
Mv mv Mv mv
-----------------------------------
R ≤25 pc 0.133 0.997 0.978 0.870
R ≤12 pc 0.188 0.696
R ≤ 8 pc 0.396 0.031
-----------------------------------
Table 4.a: Expectations for late M detections
---------------------------------------------------
log(Lx) Expected Observed Confidence
erg/s detections detections level
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27.5 9 2 0.995
28.0 7 0 0.999
28.5 3 0 0.950
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statistical results testing the working hypothesis that late M stars
follow the same cumulative X-ray luminosity function of early M stars.
Column 1 gives the chosen X-ray luminosity threshold, column 2 gives
the number of late M detections expected over the X-ray luminosity
threshold, column 3 gives the actual number of detected late M stars
over the same threshold and, column 4 is the confidence level for the
rejection of the hypothesis that the actual number of detections is
extracted from a Poisson distribution with mean equal to the expected
number.
Table 4.b: Expectations for late M detections
----------------------------------------------------
log(Fx) Expected Observed Confidence
(erg/s/cm2=mW/m2) detections detections level
----------------------------------------------------
6.4 5 1 0.966
6.6 5 0 0.993
6.8 3 0 0.950
----------------------------------------------------
Analogous to Table 4.a but using stellar X-ray surface
flux thresholds instead of X-ray luminosity.
Table 5: X-ray luminosity of young and old disk populations
Means and 1.sigma confidence level uncertainties derived from the
X-ray luminosity functions of the young-disk and old-disk star
subsamples, of the three spectral types, K, early M and late M,
respectively.
------------------------------------
Spectral Log(Lx) (erg/s)
Type young-disk old-disk
------------------------------------
K 28.0 ±0.1 27.5 ±0.1
early M 27.7 ±0.1 27.0 ±0.2
late M 27.3 ±0.1 26.9 ±0.2
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Table 6: Comparison among three different stellar age-classification methods
Wilcoxon two-sample test results for the comparison of young and old
disk stars according to three different methods of age classification:
the Eggen (U-V polygon), the |W|, and the V(pec) methods (section 4.4).
-------------------------------
Method K early M late M
-------------------------------
Eggen 0.998 0.999 0.799
V_pec 0.995 0.999 0.833
|W| 0.828 0.943 0.853
-------------------------------
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Courtesy: Marco Barbera
(End) Francois Ochsenbein [CDS] 12-Jul-1994