J/AJ/154/14 Low-mass stars in 25 Ori group and Orion OB1a (Suarez+, 2017)
New low-mass stars in the 25 Orionis stellar group and Orion OB1a sub-association from SDSS-III/BOSS spectroscopy. Suarez G., Downes J.J., Roman-Zuniga C., Covey K.R., Tapia M., Hernandez J., Petr-Gotzens M.G., Stassun K.G., Briceno C. <Astron. J., 154, 14-14 (2017)> =2017AJ....154...14S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Stars, M-type ; Photometry, VRI ; Photometry, ugriz ; Photometry, infrared ; Spectroscopy ; Spectral types ; Equivalent widths ; Effective temperatures ; Stars, masses ; Stars, ages Keywords: open clusters and associations: individual (Orion OB1a,25 Orionis) - stars: low-mass - stars: pre-main sequence Abstract: The Orion OB1a sub-association is a rich low-mass star (LMS) region. Previous spectroscopic studies have confirmed 160 LMSs in the 25 Orionis stellar group (25 Ori), which is the most prominent overdensity of Orion OB1a. Nonetheless, the current census of the 25 Ori members is estimated to be lower than 50% complete, leaving a large number of members to be still confirmed. We retrieved 172 low-resolution stellar spectra in Orion OB1a observed as ancillary science in the SDSS-III/BOSS survey, for which we classified their spectral types and determined physical parameters. To determine memberships, we analyzed the Hα emission, LiIλ6708 absorption, and NaIλλ8183,8195 absorption as youth indicators in stars classified as M type. We report 50 new LMSs spread across the 25 Orionis, ASCC18, and ASCC20 stellar groups with spectral types from M0 to M6, corresponding to a mass range of 0.10≤m/M☉≤0.58. This represents an increase of 50% in the number of known LMSs in the area and a net increase of 20% in the number of 25 Ori members in this mass range. Using parallax values from the Gaia DR1 catalog, we estimated the distances to these three stellar groups and found that they are all co-distant, at 338±66pc. We analyzed the spectral energy distributions of these LMSs and classified their disks into evolutionary classes. Using H-R diagrams, we found a suggestion that 25 Ori could be slightly older than the other two observed groups in Orion OB1a. Description: The V, R, and I photometry used in this work was obtained from the Centro de Investigaciones de Astronomia (CIDA) Deep Survey of Orion (CDSO) catalog (Downes et al. 2014, Cat. J/MNRAS/444/1793), which was constructed by coadding the multi-epoch optical observations from the CIDA Variability Survey of Orion (CVSO; Briceno et al. 2005, Cat. J/AJ/129/907). The sensitivity limits of the CDSO covers the Low-Mass Star (LMS) and Brown Dwarf (BD) population of 25 Ori and its surroundings within the region 79.7°≲α≲82.7° and 0.35°≲δ≲3.35°. The limiting magnitude of the CDSO photometry in this region is Ilim=22 and the completeness magnitude is Icom=19.6 (Downes et al. 2014, Cat. J/MNRAS/444/1793), enough to ensure an I-band detection even for the faintest targets of our spectroscopic sample (I~17.0). Additionally, we used the u, g, r, i, and z photometry from the Sloan Digital Sky Survey (SDSS) catalog (Finkbeiner et al. 2004AJ....128.2577F; Ahn et al. 2012, Cat. V/139). These values are listed in Table1. The Z, Y, J, H, and Ks near-infrared photometry used in this study was carried out by Petr-Gotzens et al. (2011Msngr.145...29P) as part of the Visible and Infrared Survey Telescope for Astronomy (VISTA) science verification surveys (Arnaboldi et al. 2010Msngr.139....6A). The 5σ limiting magnitudes of the VISTA survey of the Orion star-forming region are Z=22.5, Y=21.2, J=20.4, H=19.4, and Ks=18.6, which are enough to have VISTA photometry even for the faintest objects in our spectroscopic sample (J~15.0). Additionally, we used near-infrared photometry from the 2MASS catalog (Cutri et al. 2003, Cat. II/246) and mid-infrared photometry from IRAC-Spitzer (Hernandez et al. 2007, Cat. J/ApJ/671/1784) and the AllWISE catalog (Cutri et al. 2013, Cat. II/328). This infrared photometry is listed in Table1. The spectra used in this paper were obtained as part of the Baryon Oscillation Spectroscopic Survey (BOSS; Dawson et al. 2013AJ....145...10D), which is one of the four main surveys of SDSS (York et al. 2000AJ....120.1579Y) in its third phase (SDSS-III; Eisenstein et al. 2011AJ....142...72E). The BOSS spectrograph has plates with 1000 fibers of 2'' diameter spanning a field of view of 3.0° in diameter and covering a wavelength range from 3560Å to 10400Å with a resolution of R=1560 at 3700Å and R=2650 at 9000Å (Gunn et al. 2006AJ....131.2332G; Smee et al. 2013AJ....146...32S). File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 189 53 Photometric catalog of the confirmed members of 25 Ori or Orion OB1a table2.dat 31 53 Confirmed members and their youth indicators table3.dat 125 53 Physical parameters of the 53 confirmed members table5.dat 42 119 Stars on the Baryon Oscillation Spectroscopic Survey (BOSS) plate that were rejected as confirmed members of 25 Ori or Orion OB1a
See also: V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015) II/328 : AllWISE Data Release (Cutri+ 2013) V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012) II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) J/MNRAS/450/3490 : New brown dwarfs in Orion OB1a/25 Ori group (Downes+, 2015) J/MNRAS/444/1793 : 25 Ori group low-mass stars (Downes+, 2014) J/A+A/558/A53 : MW global survey of star clusters. II. (Kharchenko+, 2013) J/MNRAS/427/3374 : QUEST RR Lyrae Survey III. (Mateu+, 2012) J/ApJ/671/1784 : Ori OB1 IRAC/MIPS observations (Hernandez+, 2007) J/ApJ/661/1119 : Spectroscopy in the 25 Ori group (Briceno+, 2007) J/AJ/129/907 : New Ori OB1 members (Briceno+, 2005) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Star [66/158] Internal identifier of the confirmed member of 25 Ori or Orion OB1a 5- 13 F9.6 deg RAdeg Right Ascension in decimal degrees (J2000) 15- 22 F8.6 deg DEdeg Declination in decimal degrees (J2000) 24- 29 F6.3 mag umag [17.56/24.54]? The SDSS u band magnitude 31- 36 F6.3 mag gmag [15.97/21.27]? The SDSS g band magnitude 38- 43 F6.3 mag rmag [14.66/19.64]? The SDSS r band magnitude 45- 50 F6.3 mag imag [14.25/17.65]? The SDSS i band magnitude 52- 57 F6.3 mag zmag [13.48/16.59]? The SDSS z band magnitude 59- 64 F6.3 mag Vmag [15.19/20.38]? V band magnitude from the Centro de Investigaciones de Astronomia (CIDA) Deep Survey of Orion (CDSO) (1) 66- 71 F6.3 mag Rmag [14.33/19.04] R band magnitude from the CDSO (1) 73- 78 F6.3 mag Icmag [13.3/17] Ic band magnitude from the CDSO (1) 80- 85 F6.3 mag Zmag2 [13.2/16.4] Z band magnitude from VISTA (2) 87- 92 F6.3 mag Ymag2 [12.8/15.7] Y band magnitude from VISTA (2) 94- 99 F6.3 mag Jmag2 [12.28/15.12] J band magnitude from VISTA (2) 101-106 F6.3 mag Hmag2 [11.68/14.64] H band magnitude from VISTA (2) 108-113 F6.3 mag Ksmag2 [11.25/14.34] Ks band magnitude from VISTA (2) 115-120 F6.3 mag Jmag1 [12.11/15.23] 2MASS J band magnitude (3) 122-127 F6.3 mag Hmag1 [11.4/14.7] 2MASS H band magnitude (3) 129-134 F6.3 mag Ksmag1 [11/14.5] 2MASS Ks band magnitude (3) 136-141 F6.3 mag [3.6] [10/14]? Spitzer/IRAC 3.6µm (channel 1) magnitude (4) 143-148 F6.3 mag [4.5] [9.9/14]? Spitzer/IRAC 4.5µm (channel 2) magnitude (4) 150-155 F6.3 mag [5.8] [9.2/13.9]? Spitzer/IRAC 5.8µm (channel 3) magnitude (4) 157-162 F6.3 mag [8.0] [9.1/13.8]? Spitzer/IRAC 8.0µm (channel 4) magnitude (4) 164-169 F6.3 mag W1mag [10.16/14.11] AllWISE W1 (3.35µm) magnitude (5) 171-176 F6.3 mag W2mag [9.49/13.95] AllWISE W2 (4.6µm) magnitude (5) 178-183 F6.3 mag W3mag [7.14/12.55] AlLWISE W3 (11.6µm) magnitude (5) 185-189 F5.3 mag W4mag [5/9] AllWISE W4 (22.1µm) magnitude (5)
Note (1): Centro de Investigaciones de Astronomia (CIDA) Deep Survey of Orion (CDSO) catalog (Downes et al. 2014, Cat. J/MNRAS/444/1793), constructed by coadding the multi-epoch optical observations from the CIDA Variability Survey of Orion (CVSO; Briceno et al. 2005, Cat. J/AJ/129/907). Note (2): Carried out by Petr-Gotzens et al. (2011Msngr.145...29P) as part of the Visible and Infrared Survey Telescope for Astronomy (VISTA) science verification surveys (Arnaboldi et al. 2010Msngr.139....6A). Note (3): Cutri et al. 2003 (Cat. II/246). Note (4): Hernandez et al. 2007 (Cat. J/ApJ/671/1784). Note (5): AllWISE catalog (Cutri et al. 2013, Cat. II/328).
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Star [66/158] Internal identifier of the confirmed member of 25 Ori or Orion OB1a 5- 8 A4 --- SpT Spectral type 10- 12 F3.1 --- e_SpT [0.4/1.4] Spectral type uncertainty 14- 21 F8.3 0.1nm EWHa [-247.7/-2] Hα emission equivalent width (in Å) 23- 28 F6.4 0.1nm EWLi [0.079/1.72]? Li Iλ6708 absorption equivalent width (in Å) 30- 31 I2 --- NaI [-1/1]? Consistency of NaIλλ8183,8195 doublet with stellar templates (-1, 0, or 1) (6)
Note (6): For the NaIλλ8183,8195 absorption, the flags are defined as follows: -1 = The feature is consistent with an old stellar template; 0 = The feature is not conclusive; 1 = The feature is consistent with a young stellar template.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 3 I3 --- Star [66/158] Internal identifier of the confirmed member of 25 Ori or Orion OB1a 4 A1 --- Var [a]? Flag for variability candidate (7) 6- 10 F5.3 mag Av [0/4.33] Visual extinction (AV) 12- 16 F5.3 mag E_Av [0.183/1.777] Visual extinction upper uncertainty 18- 22 F5.3 mag e_Av [0/1.873] Visual extinction lower uncertainty 24- 29 F6.1 K Teff [3030.5/3806.5] Effective temperature (Teff) 31- 35 F5.1 K E_Teff [58/196] Effective temperature upper uncertainty 37- 41 F5.1 K e_Teff [56/174] Effective temperature lower uncertainty 43- 47 F5.3 Lsun Lbol [0.014/0.312] Bolometric luminosity 49- 53 F5.3 Lsun E_Lbol [0.01/0.2] Bolometric luminosity upper uncertainty 55- 59 F5.3 Lsun e_Lbol [0.008/0.221] Bolometric luminosity lower uncertainty 61- 65 F5.3 Msun Mass [0.098/0.573] Mass 67- 71 F5.3 Msun E_Mass [0.016/0.115] Mass upper uncertainty 73- 77 F5.3 Msun e_Mass [0.019/0.125] Mass lower uncertainty 79- 84 F6.3 Myr Age [0.506/14.128] Age 86- 91 F6.3 Myr E_Age [0.742/12.817]? Age upper uncertainty 93- 97 F5.3 Myr e_Age [0.116/9.579]? Age lower uncertainty 99-102 A4 --- TTS T Tauri star (TTS) classification (CTTS or WTTS) (8) 104-111 A8 --- Disk Disk evolutionary classification (ClassII, ClassIII, Evolved, or TDC=Transitional Disk Candidate) (9) 113-125 A13 --- Group Stellar group designation (25 Ori, ASCC 18, ASCC 20 or outside these groups) (10)
Note (7): a=the member is a >99% probable variable star according to the Centro de Investigaciones de Astronomia (CIDA) Variability Survey of Orion (CVSO; Briceno et al. 2005, Cat. J/AJ/129/907; Mateu et al. 2012, Cat. J/MNRAS/427/3374). Note (8): T Tauri star classes are defined as follows: CTTS = Classical T Tauri star; WTTS = Weak T Tauri star. Note (9): The members classification is defined as follows: ClassII = We classified the members as Class II when their infrared Spectral Energy Distributions (SEDs) resembled the median SEDs of Class II disks of the σ Orionis cluster (Hernandez et al. 2007, Cat. J/ApJ/662/1067) and the Taurus star-forming region (Furlan et al. 2006ApJS..165..568F); ClassIII = The members whose infrared Spectral Energy Distributions (SEDs) were consistent with the photospheric Baraffe et al. (2015A&A...577A..42B) model fit; Evolved = The members showing lower infrared excesses; TDC = Transitional Disk Candidates (members whose near-infrared Spectral Energy Distribution (SED) was consistent with evolved systems or Class III objects but which had an unexpectedly strong excess at 22µm). Note (10): Outside location label indicates the member not belonging to any stellar group defined by Kharchenko et al. 2013 (Cat. J/A+A/558/A53).
Byte-by-byte Description of file: table5.dat
Bytes Format Units Label Explanations
1- 9 F9.6 deg RAdeg Right Ascension in decimal degrees (J2000) 11- 18 F8.6 deg DEdeg Declination in decimal degrees (J2000) 20- 23 A4 --- SpT Spectral type 25- 27 F3.1 --- e_SpT [0.5/8.3]? Spectral type uncertainty 29 A1 --- f_SpT [a] Spectral type reference (1) 31- 36 F6.3 mag Imag [13/19.5]? Ic magnitude from the Centro de Investigaciones de Astronomia (CIDA) Deep Survey of Orion (CDSO) catalog (Downes et al. 2014, Cat. J/MNRAS/444/1793) 38- 42 F5.3 mag I-J [0/1.747]? Ic-J color index from the CIDA Deep Survey of Orion (CDSO) and VISTA catalogs
Note (1): a=The spectral type reported was assigned by the SDSS classification, which has not assigned the spectral type uncertainties. When null value is present, the spectral type was assigned in this work using the SPTCLASS code (http://www.cida.gob.ve/~hernandj/SPTclass/sptclass.html).
History: From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 27-Sep-2017
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