J/MNRAS/356/1583 RV of Sigma Ori low-mass candidate members (Burningham+, 2005)
Contamination and exclusion in the σ Orionis young group. Burningham B., Naylor T., Littlefair S.P., Jeffries R.D. <Mon. Not. R. Astron. Soc., 356, 1583-1591 (2005)> =2005MNRAS.356.1583B
ADC_Keywords: Clusters, open ; Stars, pre-main sequence ; Stars, dwarfs ; Radial velocities ; Equivalent widths Keywords: techniques: radial velocities - techniques: spectroscopic - stars: low-mass, brown dwarfs - stars: pre-main-sequence - open clusters and associations: individual: σ Orionis Abstract: We present radial velocities for 38 low-mass candidate members of the σ Orionis young group. We have measured their radial velocities by cross-correlation of high-resolution (R\gl6000) AF2/Wide Field Fibre Optical Spectrograph (WYFFOS) spectra of the gravity-sensitive NaI doublet at 8183,8195Å, on the nights of 2003 January 3 and 4. The total sample contained 117 objects, of which 54 have sufficient signal-to-noise ratio to detect NaI at an equivalent width of 3Å; however, we only detect NaI in 38 of these. This implies that very low-mass members of this young group display weaker NaI absorption than similarly aged objects in the Upper Scorpius OB association. We develop a technique to assess membership using radial velocities with a range of uncertainties that does not bias the selection when large uncertainties are present. The resulting membership probabilities are used to assess the issue of exclusion in photometric selections, and we find that very few members are likely to be excluded by such techniques. We also assess the level of contamination in the expected pre-main-sequence region of colour-magnitude space brighter than I=17. We find that contamination by non-members in the expected pre-main-sequence region of the colour-magnitude diagram is small. We conclude that although radial velocity alone is insufficient to confirm membership, high signal-to-noise ratio observations of the NaI doublet provide the opportunity to use the strength of NaI absorption in concert with radial velocities to asses membership down to the lowest masses, where lithium absorption no longer distinguishes youth. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table3.dat 98 54 Equivalent widths and radial velocities measured using the NaI doublet.
See also: J/MNRAS/356/89 : sigma Ori low-mass stars (Kenyon+, 2005) J/AJ/128/2316 : BVRIJHKs photometry in sigma Ori cluster (Sherry+, 2004) J/A+A/419/249 : RJHKs phot. of sigma Ori low-mass stars (Scholz+, 2004) J/AN/325/705 : RIJHKs of low-mass stars in sigma Ori (Bejar+, 2004) Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 4 F4.2 --- Field Field number (1) 6- 9 I4 --- Star Object number (1) 11- 12 I2 h RAh Right ascension (J2000) 14- 15 I2 min RAm Right ascension (J2000) 17- 22 F6.3 s RAs Right ascension (J2000) 24 A1 --- DE- Declination sign (J2000) 25- 26 I2 deg DEd Declination (J2000) 28- 29 I2 arcmin DEm Declination (J2000) 31- 35 F5.2 arcsec DEs Declination (J2000) 37- 42 F6.3 mag Icmag Cousins I magnitude 44- 48 F5.3 mag e_Icmag rms uncertainty on Imag 50- 51 A2 --- q_Icmag Quality flag in Icmag (2) 53- 57 F5.3 0.1nm Rc-Ic Cousins R-I colour index 59- 63 F5.3 0.1nm e_Rc-Ic rms uncertainty on Rc-Ic 65- 66 A2 --- q_Rc-Ic Quality flag in Rc-Ic (2) 68- 72 F5.2 km/s EW Equivalent width of NaI doublet (8183/8195Å) integrated over the range 8180-8202Å (3) 74- 77 F4.2 km/s e_EW rms uncertainty on EW 79- 84 F6.2 km/s RVbar ?=- Barycentric radial velocity (4) 85 A1 --- f_RVbar [X] X=cross-correlation failed 87- 91 F5.2 % e_RVbar ?=- rms uncertainty on RVbar 93- 98 F6.2 % Pvel ?=- Membership probability from velocity measurements
Note (1): The field number and object number are those used in the photometric catalog of Kenyon et al. (2005, Cat. J/MNRAS/356/89, file "catalog.dat"). Objects identified in Simbad as [KJN2005] F.FF NNNN Note (2): Quality flags are as described in Burningham et al. (2003, cat. J/MNRAS/346/1143) as follows: OO = OK for Vmag and Icmag OV = OK for Vmag, Variable for Icmag VV = Variable for Vmag and Icmag Note (3): The continuum was measured from bands at 8151-8173 and 8233-8255Å. Note (4): Radial velocities were measured by cross-correlating against GJ3517, and corrected to give barycentric radial velocities.
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 13-Mar-2006
|The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line|