J/AJ/108/538 Metal-poor MS stars UBV photometry (Preston+ 1994)
The space density and kinematics of blue metal-poor main sequence stars
near the solar circle
Preston G.W., Beers T.C., Shectman S.A.
<Astron. J. 108, 538 (1994)>
=1994AJ....108..538P 1994AJ....108..538P
ADC_Keywords: Stars, blue ; Stars, metal-deficient ; Photometry, UBV ;
Radial velocities
Abstract:
From analysis of a photometrically selected sample of 175 metal-poor
field stars with main sequence gravities (hereafter BMPs) and UBV
colors blueward of the most metal-poor globular cluster main-sequence
turnoffs, 0.15<(B-V)0<0.35, and properties of the candidate lists of
the HK objective prism survey, we calculate the space density and a
suitably defined specific frequency of BMPs within ∼2kpc of the Sun.
We consider two cases. If we adopt the luminosities and color
distribution of globular cluster blue stragglers (hereafter BS) for
BMPs, the BMP space density, is ∼350kpc-3, from which we obtain a
specific frequency S(BMP)∼8, a value 9 times larger than that of BSs
in globular clusters. From this result, we conclude that cluster-type
BSs are but a minor component of the field BMPs and that the remainder
must be of a different nature. If we adopt luminosities of metal-poor
models halfway between the Zero Age Main Sequence and the phase of
core hydrogen exhaustion, we obtain a space density of
450(+300,-150)kpc-3 and a specific frequency S(BMP)=10(+5,-3).
From a subsample of 107 BMPs with available radial velocities we
derive a galactic rotation of 128km/s and an isotropic velocity
dispersion of σ∼90km/s, values intermediate between those of
halo and thick-disk populations. From analysis of a larger sample of
stars on 0.15<(B-V)0<0.35 binned by a crude line-blanketing parameter,
we find that our results are insensitive to adopted BMP selection
criteria: none of these subsamples of A- and early F-type stars above
the galactic plane possess disk kinematics. The region of the
UBV two-color diagram occupied by BMPs could be populated by
metal-deficient, main-sequence gravity stars with ages substantially
younger than those of the metal-poor halo. Because we cannot imagine
how or where the observed local population of BMPs could have been
produced within our galaxy during the past 3 to 10Gyr, we suggest that
BMPs are the bluest members of metal-poor intermediate-age main
sequences accreted, probably, from dwarf spheroidal satellites of the
Milky Way during the past 10Gyr. We discuss observational consequences
of this suggestion.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 60 175 BMP stars identified photometrically in the HK survey
table9.dat 29 219 New UBV observations of HK survey stars
table10.dat 34 47 Repeat UBV observations of HK survey stars
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See also:
J/AJ/87/1515 : UBV photometry of AB stars in halo (Pier, 1982)
J/ApJS/53/791 : Spectroscopy of AB stars in halo (Pier, 1983)
J/AJ/90/2089 : Stars of very low metal abundance. (Beers+, 1985)
J/PASP/102/1392 : UBV photometry from HK survey. (Doinidis+ 1990)
J/PASP/103/973 : Photoelectric UBV from HK survey. (Doidinis+ 1991)
J/ApJS/76/1001 : UBV photometry of HK survey stars (Preston+, 1991)
J/AJ/103/267 : Spectrocopy of hot stars in galactic halo (Beers+ 1992)
J/AJ/103/1987 : Stars of very low metal abundance (Beers+ 1992)
J/AJ/108/268 : HK survey emission-line candidates positions (Beers+ 1994)
J/AJ/112/1188 : HK survey emission-line candidates (Beers+ 1996)
J/AJ/117/2329 : Spectroscopy of hot stars in the halo. (Wilhelm+, 1999)
J/ApJS/123/639 : UBV photometry of metal-weak candidates (Norris+, 1999)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- BPS-CS Star identification in HK survey (field-number)
11- 15 F5.1 deg GLON Galactic longitude
17- 21 F5.1 deg GLAT Galactic latitude
23- 27 F5.3 mag E(B-V) (B-V) colour excess adopted estimate
29- 33 F5.2 mag V0 Reddening-corrected apparent V magnitude
35- 39 F5.3 mag (B-V)0 Reddening-corrected B-V colour index
41- 46 F6.3 mag (U-B)0 Reddening-corrected U-B colour index
48- 51 F4.2 --- D0 Color parameter (1)
53- 56 I4 km/s HRV ? Heliocentric radial velocity
58 I1 --- r_HRV ? Reference for heliocentric radial velocity (2)
60 I1 --- r_UBV ? Reference for UBV data (2)
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Note (1): D0 is the perpendicular distance of each star from the linearized
two-color main sequence relation for [Fe/H]=0.0 in the
(U-B)0 vs (B-V)0 plane.
Note (2): References are numbered as follows:
1 = Beers et al., 1992, Cat. J/AJ/103/267
2 = Beers et al., 1992, Cat. J/AJ/103/1987
3 = Preston et al., 1991, Cat J/ApJS/76/1001
4 = This paper
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Byte-by-byte Description of file: table9.dat table10.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- BPS-CS Star identification in HK survey (field-number)
11- 15 F5.2 mag Vmag Johnson V magnitude
17- 22 F6.3 mag B-V Johnson B-V colour index
24- 29 F6.3 mag U-B Johnson colour index
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History:
* 21-Mar-1997: Prepared via OCR at CDS.
* 17-Dec-2005: ReadMe file revisited
(End) James Marcout, Patricia Bauer [CDS] 21-Mar-1997