J/ApJS/191/389 Photometric monitoring in σ Ori cluster (Cody+, 2010)
Precision photometric monitoring of very low mass σ Orionis cluster members: variability and rotation at a few Myr. Cody A.M., Hillenbrand L.A. <Astrophys. J. Suppl. Ser., 191, 389-422 (2010)> =2010ApJS..191..389C
ADC_Keywords: Cross identifications ; Photometry, infrared ; Clusters, globular ; Stars, variable Keywords: brown dwarfs - open clusters and associations: individual (σ Orionis) - protoplanetary disks - stars: low-mass - stars: rotation - stars: variables: T Tauri, Herbig Ae/Be - techniques: photometric Abstract: We present high-precision photometry on 107 variable low-mass stars and brown dwarfs in the ∼3Myr σ Orionis open cluster. We have carried out I-band photometric monitoring within two fields, encompassing 153 confirmed or candidate members of the low-mass cluster population, from 0.02 to 0.5M☉. We are sensitive to brightness changes on timescales from 10 minutes to two weeks with amplitudes as low as 0.004mag, and find variability on these timescales in nearly 70% of cluster members. We identify both periodic and aperiodic modes of variability, as well as semi-periodic rapid fading events that are not accounted for by the standard explanations of rotational modulation of surface features or accretion. We have incorporated both optical and infrared color data to uncover trends in variability with mass and circumstellar disks. Description: A field centered on J053800.6-024346.3 in the σ Orionis cluster was observed for 12 consecutive nights from 2007 December 27 to 2008 January 7 with the CTIO 1.0m telescope and Y4KCam detector. A second field at J053931.2-023725.9 was observed from 2008 December 14 to 24. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 171 153 *σ Orionis cluster : confirmed and candidate members in our photometric sample table2.dat 78 147 Photometry of confirmed and candidate cluster members in the sample table3.dat 54 84 Objects with detected I-band periodic variability table4.dat 53 42 Objects with detected I-band aperiodic variability
Notes on table1.dat: We do not list objects that are saturated in our photometry or were presented in previous membership surveys but later determined to be non-members.
See also: II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003) J/A+A/478/667 : The Mayrit catalogue (Caballero, 2008) J/MNRAS/385/2210 : Spectroscopy around lam Ori and sig Ori (Maxted+, 2008) J/A+A/488/167 : Low-mass stars in σ Ori and λ Ori (Sacco+, 2008) J/ApJ/662/1067 : Sptizer observations of sigma Orionis (Hernandez+, 2007) J/A+A/446/501 : XMM observations of sigma Ori cluster (Franciosini+, 2006) J/MNRAS/356/1583 : RV of Sigma Ori low-mass candidate members (Burningham+, 2005) J/MNRAS/356/89 : sigma Ori low-mass stars (Kenyon+, 2005) J/A+A/419/249 : RJHKs photometry of sigma Ori low-mass stars (Scholz+, 2004) J/AJ/128/2316 : BVRIJHKs photometry in sigma Ori cluster (Sherry+, 2004) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name 2MASS or CTIO name (JHHMMSSss+DDMMSSs) or S Ori JHHMMSS.s+DDMMSS name 25- 91 A67 --- OName Other designations (1) 93- 96 A4 --- SpT MK spectral type 98-102 A5 --- SpT2 MK spectral type from litterature 104 I1 --- r_SpT2 ? Reference for SpType2 (4) 106 A1 --- Var [Y] for variable 108-115 A8 --- r_Var Reference(s) for Var (4) 117-144 A28 --- MmE Membership explanation(s) (2) 146-147 A2 --- NMmE Possible non-member explanation (2)(3) 149-152 A4 --- r_NMmE Reference(s) for possible non-membership (4) 154-171 A18 --- r_MmE Reference(s) for membership (4)
Note (1): Alternate identifications based on previous membership surveys of the cluster: S Ori = Bejar et al. (1999ApJ...521..671B; <[BZR99] S Ori NN> in Simbad or 2001ApJ...556..830B; <[BMZ2001] S Ori JHHMMSS.s+DDMMSS> in Simbad); note that based on the finder chart provided in 1999 reference, we conclude that S Ori 26 is incorrectly identified by Lodieu et al. (2009A&A...505.1115L); the actual object is their UGCS J053915.76-023826.3, a proper-motion selected σ Ori member. r = Wolk's (1996PhDT........63W) X-ray-selected source list 4771 = Wolk's (1996PhDT........63W) X-ray-selected source list SO = Hernandez et al.'s (2007, Cat. J/ApJ/662/1067; <[HHM2007] NNNN> in Simbad) list of candidate cluster members Mayrit = Mayrit catalog compiled by Caballero (2008, Cat. J/A+A/478/667; <Mayrit NNNNNNN> in Simbad). SWW = Sherry et al. (2004, Cat. J/AJ/128/2316; <[SWW2004] JHHMMSS.sss+DDMMSS.ss> in Simbad); note that several of the objects identified in this reference are duplicated and thus only included once here (SWW103 is SWW207; SWW126 is SWW162). KJN = Kenyon et al. (2005, Cat. J/MNRAS/356/89; <[KJN2005] NN> in Simbad), SE = Scholz & Eisloffel (2004, Cat. J/A+A/419/249; <[SE2004] NNN> in Simbad), M = Maxted et al. (2008, Cat. J/MNRAS/385/2210; <[MJO2008] JHHMMSS.s+DDMMSS> in Simbad), B = Burningham et al. (2005, Cat. J/MNRAS/356/1583), F = Franciosini et al. (2006, Cat. J/A+A/446/501). Source HH446 is from Andrews et al. (2004ApJ...606..353A). The six objects without IDs were found in this work (see Section 7.1.1). Note (2): The membership evidence column refers to photometric and spectroscopic measurements that confirm the object's youth and/or cluster membership. For exemple, membership evidence as follows: Halpha = Hα emission line indicative of low gravity Na = Na emission line indicative of low gravity, FL = forbidden emission lines (OI, NII, SII), Li = presence of Li absorption, vr = radial velocity consistent with the σ Ori mean (27<vr<37km/s; Jeffries et al. 2006MNRAS.371L...6J), D = infrared excess from Spitzer indicative of a disk; disks noted as "(EV)" or "(TD)" refer to evolved and transitional disks, respectively, as classified by Hernandez et al. (2007, Cat. J/ApJ/662/1067). (PM) = proper motion consistent with σ Ori membership (we have applied parentheses since this latter criterion is not enough to definitively select members but is useful for eliminating some non-members). Note (3): Objects with evidence both for and against membership with the specific criterion suggesting non-membership. Note (4): References as follows: 1 = Barrado y Navascues et al. 2003A&A...404..171B; 2 = Sacco et al. 2008, Cat. J/A+A/488/167; 3 = Zapatero Osorio et al. 2002A&A...384..937Z; 4 = Kenyon et al. 2005, Cat. J/MNRAS/356/89; 5 = Muzerolle et al. 2003ApJ...592..266M; 6 = Caballero et al. 2006A&A...445..143C; 7 = Caballero et al. 2008A&A...491..515C; 8 = Caballero et al. 2007A&A...470..903C; 9 = Maxted et al. 2008, Cat. J/MNRAS/385/2210; 10 = Burningham et al. 2005, Cat. J/MNRAS/356/1583; 11 = Scholz & Eisloffel 2004, Cat. J/A+A/419/249; 12 = Lodieu et al. 2009A&A...505.1115L; 13 = Hernandez et al. 2007, Cat. J/ApJ/662/1067; 14 = Luhman et al. 2008ApJ...688..362L; note that while this reference did not explicitly list which stars have infrared excesses indicative of disks, we have used their photometry (derived from Spitzer images acquired by Hernandez et al. 2007, Cat. J/ApJ/662/1067 and Scholz & Jayawardhana, 2008ApJ...672L..49S) to identify disk-bearing candidates (Section 7.4). Unsurprisingly, we recover all but one of the disks already identified by Caballero et al. (2007A&A...470..903C) and Hernandez et al. (2007, Cat. J/ApJ/662/1067) from the same images. We therefore do not include Luhman et al. (2008ApJ...688..362L) in our disk references, except in the case of the one newly identified disk-bearing object, 2MASS J05375398-0249545. 15 = Caballero et al. 2004A&A...424..857C; 16 = Bailer-Jones & Mundt 2001A&A...367..218B; 17 = Zapatero Osorio et al. 2003A&A...408..663Z.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name 2MASS JHHMMSSss+DDMMSSs or S Ori JHHMMSS.s+DDMMSS designation 25- 29 F5.2 mag Rcmag Cousins R-band magnitude 31- 34 F4.2 mag e_Rcmag Rcmag uncertainty 36- 40 F5.2 mag Icmag Cousins I-band magnitude 42- 45 F4.2 mag e_Icmag Icmag uncertainty 47- 51 F5.2 mag Jmag ? 2MASS J-band magnitude 53- 56 F4.2 mag e_Jmag ? Jmag uncertainty 58- 62 F5.2 mag Hmag ? 2MASS H-band magnitude 64- 67 F4.2 mag e_Hmag ? Hmag uncertainty 69- 73 F5.2 mag Ksmag ? 2MASS Ks-band magnitude 75- 78 F4.2 mag e_Ksmag ? Ksmag uncertainty
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name 2MASS or CTIO identification (JHHMMSSss+DDMMSSs) 25- 29 F5.2 d Per Period 31- 34 F4.2 d e_Per 3σ period uncertainty 36- 40 F5.3 mag Amp Amplitude 42- 46 F5.3 mag e_Amp 3σ amplitude uncertainty 48- 50 A3 --- Vtype Variable type (1) 52 A1 --- Mm [YMN] Membership (2) 54 A1 --- f_Mm [a-d] Flag on Mm (3)
Note (1): Variable type, based on light curve appearance, as follows: EB = likely eclipsing binaries S = fairly sinusoidal U = periodic but specific shape unknown due to noise or other features, O = or other distinct shape, such as that of a pulsator. S/U = mostly sinusoidal but has interesting blip-like features over short timescale. Note (2): Membership according to the following: Y = confirmed cluster member: has either broad Hα in emission, Li in absorption, weak alkali absorption lines (e.g., Na), forbidden emission lines (e.g., OI, NII, SII), or infrared excess indicative of a disk, as listed in Table 1. M = ("Maybe") possible member: object with only proper motions, only variability, no spectroscopic data, or conflicting membership indicators. N = non-member: target whose colors are too blue to be sufficiently young for σ Ori and whose variability type is indicative of a field eclipsing binary or pulsator. Note (3): Flags as follows: a = With I=13.43±0.01 and R=13.96±0.02, and a simple periodic light curve, this object is a candidate σ Ori member; but since its colors fall at the blue edge of the cluster sequence, we emphasize that this is a tentative identification. b = This object is a new candidate BD, with I=18.37±0.04 and R=20.19±0.08 c = This object is a new candidate BD, with I=18.27±0.05 and R=20.25±0.08 d = We identify this object as a new candidate σ Ori member, with I=17.04±0.03 and R=18.72±0.04.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 23 A23 --- Name 2MASS identification (JHHMMSSss+DDMMSSs) 25- 28 F4.2 mag Amp Peak-to-peak amplitude 30- 33 F4.2 mag e_Amp Amplitude rms 35 A1 --- Mm [YM] Membership (1) 37 A1 --- f_Mm [ab] Flag on Mm (2) 39- 45 F7.2 0.1nm EW ? Hα equivalent width 47- 51 F5.2 0.1nm e_EW ? EW uncertainty 53 A1 --- r_EW [1-4] Reference for EW (3)
Note (1): Membership as in table 3, with the following meaning: Y = Confirmed cluster member M = Possible member Note (2): New candidate cluster members based on their position in the color-magnitude diagram and light curve rms indicative of variability. Their magnitudes are as follows: a = I∼12.6 (2MASS J05385946-0242198) and b = I∼12.9 (2MASS J05392307-0228112). Note (3): References as follows: 1 = Caballero et al. 2008A&A...491..515C; 2 = Sacco et al. 2008, Cat. J/A+A/488/167; 3 = Zapatero Osorio et al. 2002A&A...384..937Z; 4 = Caballero et al. 2007A&A...470..903C
History: From electronic version of the journal
(End) Emmanuelle Perret [CDS] 19-Jan-2011
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