J/AJ/120/479 Low-mass stars in the Upper Sco association (Ardila+, 2000)
A survey for low-mass stars and brown dwarfs in the Upper Scorpius
OB association.
Ardila D., Martin E., Basri G.
<Astron. J., 120, 479-487 (2000)>
=2000AJ....120..479A 2000AJ....120..479A
ADC_Keywords: Stars, pre-main sequence
Keywords: open clusters and associations: individual (Scorpius-Centarus);
stars: low-mass, brown dwarfs
Abstract:
The Upper Scorpius association is the OB association nearest to the
Sun (145pc). Its young age (∼5Myr) makes it an ideal place to search
for low-mass stars and brown dwarfs, as these objects should be
relatively bright. We have performed a photometric search for the
low-mass members of the association, using the R, I, and Z filters.
The completeness limit is I∼18.5, and the saturation limit is I∼13.
We obtain 138 candidate members, covering nearly the entire M spectral
type range. We find an excess of brown dwarf candidates over the
number predicted by a Miller-Scalo initial mass function. In addition,
we have performed infrared imaging and low-resolution optical
spectroscopy of selected candidates. We find that the infrared
observations confirm the spectral types obtained with the optical
photometry. Furthermore, we find Hα in emission in 20 of the 22
objects observed spectroscopically. As Hα is an indicator of
youth, we believe that these 20 objects may belong to the association.
One of them, UScoCTIO 128, has a very strong and constant Hα
line (equivalent width -130Å), and its position in the
color-magnitude diagram suggests that it is a brown dwarf with mass
0.02M☉. Confirmation of this and the other candidates will
have to wait for higher resolution observations that can reveal
spectroscopic mass indicators such as LiI and gravity indicators such
as KI and the subordinate lines of NaI.
Description:
We obtained photometry for eight fields of 80x80arcmin in Upper Sco
using the 60cm Michigan Curtis Schmidt telescope at Cerro Tololo
Inter-American Observatory (CTIO), on 1998 April 1-5.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 64 138 RIZ candidate members in the Upper Scorpius OB
association
table3.dat 69 26 Spectroscopic observations
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See also:
J/MNRAS/373/95 : ZYJHK survey of Upper Sco association (Lodieu+, 2006)
J/MNRAS/374/372 : ZYJHK photometry in Upper Sco (Lodieu+, 2007)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- --- [UScoCTIO]
10- 12 I3 --- UScoCTIO Star number
17- 18 I2 h RAh Right Ascension J2000 (hours)
20- 21 I2 min RAm Right Ascension J2000 (minutes)
23- 27 F5.2 s RAs Right Ascension J2000 (seconds)
29 A1 --- DE- Declination J2000 (sign)
30- 31 I2 deg DEd Declination J2000 (degrees)
33- 34 I2 arcmin DEm Declination J2000 (minutes)
36- 39 F4.1 arcsec DEs Declination J2000 (seconds)
44- 48 F5.2 mag Imag CTIO I magnitude
50- 53 F4.2 mag e_Imag rms uncertainty on Imag
56- 59 F4.2 mag R-I CTIO R-I colour index
61- 64 F4.2 mag e_R-I rms uncertainty on R-I
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- --- [UScoCTIO]
10- 12 I3 --- UScoCTIO Star number
14 A1 --- l_EWHa Limit flag on EWHa
15- 20 F6.1 0.1nm EWHa ?=- Hα equivalent width (1)
22- 25 A4 --- SpType Spectral type
(accuracy is half a spectral subclass)
27- 29 F3.1 mag AV ?=- Reddening (accuracy is 0.5mag)
31- 34 F4.2 mag R-I CTIO R-I colour index (2)
36- 39 F4.2 mag e_R-I rms uncertainty on R-I
41- 46 F6.3 mag Jmag ?=- CIRIM J magnitude
48- 51 F4.2 mag e_Jmag ?=- rms uncertainty on Jmag
53- 58 F6.3 mag Hmag ? CIRIM H magnitude
60- 63 F4.2 mag e_Hmag ? rms uncertainty on Hmag
65- 69 A5 --- SpType2 Spectral type from the I-J colour
(Kirkpatrick & McCarthy, 1994AJ....107..333K 1994AJ....107..333K)
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Note (1): The upper limits are nondetections.
Note (2): R-I colour, with reddening correction applied (if known)
from Cardelli, Clayton, & Mathis (1989ApJ...345..245C 1989ApJ...345..245C)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 12-Feb-2008