J/MNRAS/356/89 sigma Ori low-mass stars (Kenyon+, 2005)
Membership, binarity and accretion among very low-mass stars and brown dwarfs
of the σ Orionis cluster.
Kenyon M.J., Jeffries R.D., Naylor T., Oliveira J.M., Maxted P.F.L.
<Mon. Not. R. Astron. Soc., 356, 89-106 (2005)>
=2005MNRAS.356...89K 2005MNRAS.356...89K
ADC_Keywords: Clusters, open ; Stars, pre-main sequence ; Stars, dwarfs ;
Radial velocities ; Equivalent widths ; Photometry
Keywords: techniques: radial velocities - techniques: spectroscopic -
stars: low-mass, brown dwarfs - stars: pre-main-sequence -
open clusters and associations: individual: sigma Orionis
Abstract:
Intermediate-resolution (R∼7000) spectroscopy is presented for
76 photometrically selected very low-mass (0.04<M<0.3M☉)
candidate members of the young cluster around sigma Orionis (sigma
Ori). More than two-thirds appear to be genuine cluster members on the
basis that they exhibit Li I 6708Å absorption, weak Na I
8183/8195Å features and a radial velocity consistent with the
cluster mean. Photometric selection alone therefore appears to be very
effective in identifying cluster members in this mass range. Only six
objects appear to be certain non-members; however, a substantial
subset of 13 candidates have ambiguous or contradictory indications of
membership and lack Li absorption. Together with an observed spread in
the equivalent width of the Li absorption feature in the cooler stars
of our sample, this indicates that there may be deficiencies in our
understanding of the formation of this line in cool, low-gravity
objects.
Description:
We observed the field around sigma Ori with the Wide Field Camera
(WFC) on the 2.5-m Isaac Newton Telescope using Harris R and Sloan i
filters on the nights of 1999 September 2730.
Spectra were obtained with the Wide Field Fiber Optic Spectrograph
(WYFFOS) mounted at the Nasmyth focus of the 4.2-m William Herschel
Telescope during the nights of 1999 December 11 and 12.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 85 41001 *RI photometry in the region of σ Ori
flags.dat 84 18 Flags
members.dat 133 57 Members of the sigma Ori cluster
nonmemb.dat 101 6 Non-members of the sigma Ori cluster
uncert.dat 133 13 Uncertain membership
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Note on catalog.dat: this catalogue, which is the source of the
photometric plots presented in the paper, was added in
April 2007 (see the "History" section below)
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See also:
J/MNRAS/356/1583 : Sigma Ori low-mass candidate members (Burningham+, 2005)
J/A+A/419/249 : RJHKs phot. of sigma Ori low-mass stars (Scholz+, 2004)
J/AJ/128/2316 : BVRIJHKs photometry in sigma Ori cluster (Sherry+, 2004)
J/AN/325/705 : RIJHKs of low-mass stars in sigma Ori (Bejar+, 2004)
J/MNRAS/346/1143 : VI photometry of Collinder 121 (Burningham+, 2003)
J/MNRAS/351/1401 : RcIcZ photometry of NGC 2547 (Jeffries+, 2004)
J/A+A/436/853 : IR phot. of Alpha Per low-mass members (Lodieu+, 2005)
J/MNRAS/358/341 : Ic photometry of IC 348 (Littlefair+, 2005)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 4 F4.2 --- Field Field and CCD number (1)
6- 10 I5 --- Star Star number in the field
12- 13 I2 h RAh Right ascension (J2000)
15- 16 I2 min RAm Right ascension (J2000)
18- 23 F6.3 s RAs Right ascension (J2000)
25 A1 --- DE- Declination sign (J2000)
26- 27 I2 deg DEd Declination (J2000)
29- 30 I2 arcmin DEm Declination (J2000)
32- 36 F5.2 arcsec DEs Declination (J2000)
38- 45 F8.3 pix Xpos X position
47- 54 F8.3 pix Ypos Y position
56- 61 F6.3 mag Icmag ?=0.000 Cousins I magnitude
63- 68 F6.3 mag e_Icmag ?=99.999 rms uncertainty on Icmag
70 A1 --- f_Icmag Flag for Icmag (in flag.dat file; O=OK)
71 A1 --- fR Flag for Rcmag (in flag.dat file; O=OK)
73- 78 F6.3 mag Rc-Ic ?=99.999 Cousins R-I colour index
80- 85 F6.3 mag e_Rc-Ic ?=99.999 rms uncertainty on R-I
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Note (1): The number after the decimal is the CCD number.
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Byte-by-byte Description of file: flags.dat
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Bytes Format Units Label Explanations
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1 A1 --- Flag Flag code (1)
3- 49 A47 --- Expla Flag meaning
51- 75 A25 --- Algo Algorithm used
77- 82 A6 --- Type Type (Strong or Weak)
84 I1 --- FNum ? Flag number for the older versions of
the software
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Note (1): If a star is flagged as having negative counts (M), the
magnitude is replaced with the uncertainty in flux converted into
magnitudes. Thus magnitudes for objects flagged M should be treated
as bright (i.e. lower) limits. It also means that colours which are
quoted for these objects are limits.
For example a flag of MO in the B-V colour, means that the B magnitude
is a lower limit, so B-V is a lower limit. The uncertainty becomes
meaningless, unless you want the description for real aficionados...
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Byte-by-byte Description of file: members.dat nonmemb.dat uncert.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- [KJN2005] Sequential number
4- 5 I2 h RAh Right ascension (J2000)
7- 8 I2 min RAm Right ascension (J2000)
10- 14 F5.2 s RAs Right ascension (J2000)
16 A1 --- DE- Declination sign (J2000)
17- 18 I2 deg DEd Declination (J2000)
20- 21 I2 arcmin DEm Declination (J2000)
23- 27 F5.2 arcsec DEs Declination (J2000)
29- 33 F5.2 mag Icmag Cousins I magnitude
35- 38 F4.2 mag e_Icmag rms uncertainty on Icmag
40- 41 A2 --- f_Icmag [OO] OO: OK
44- 47 F4.2 mag Rc-Ic Cousins R-I colour index
49- 52 F4.2 mag e_Rc-Ic rms uncertainty on Rc-Ic
54- 55 A2 --- f_Rcmag [OO] OO: OK
57- 59 I3 km/s HRV1 ? Heliocentric radial velocity on night 1
61 I1 km/s e_HRV1 ? rms uncertainty on HRV1
63- 64 A2 --- f_HRV1 [OO AA] OO: OK, AA: Absent input data
67- 68 I2 km/s HRV2 ? Heliocentric radial velocity on night 2
70 I1 km/s e_HRV2 ? rms uncertainty on HRV2
72- 73 A2 --- f_HRV2 [OO AA] OO: OK, AA: Absent input data
76- 79 F4.2 0.1nm EWLi ? LiI (6708Å) equivalent width
81- 84 F4.2 0.1nm e_EWLi ? rms uncertainty on EWLi
86- 87 A2 --- f_EWLi [OO UU] OO: OK, UU: Uncertain
90- 93 F4.2 0.1nm EWNa ? NaI (8183/8195Å) equivalent width
95- 98 F4.2 0.1nm e_EWNa ? rms uncertainty on EWNa
100-101 A2 --- f_EWNa [OO] OO: OK
103-124 A22 --- [BMZ2001] Name from Bejar et al. (2001ApJ...556..830B 2001ApJ...556..830B)
S Ori JHHMMSS.s+DDMMSS
126-133 A8 --- [BZR99] Name from Bejar et al. (1999ApJ...521..671B 1999ApJ...521..671B)
S Ori NN
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History:
* 28-Apr-2005: Copied at
http://www.astro.ex.ac.uk/people/timn/Catalogues/description.html
* 27-Mar-2006 : Cross-identifications [BMZ2001] and [BZR99] added
(from printed version)
* 05-Apr-2007: the whole catalog (file "catalog.dat") was added, from
http://www.astro.ex.ac.uk/people/timn/Catalogues/KJNOM2005/sori_ri.cat
(End) Patricia Vannier [CDS] 28-Apr-2005