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 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:
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FileName Lrecl Records Explanations
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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
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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.
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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
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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)
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Note (1): Alternate identifications based on previous membership surveys
of the cluster:
S Ori = Bejar et al. (1999ApJ...521..671B 1999ApJ...521..671B; <[BZR99] S Ori NN> in Simbad or
2001ApJ...556..830B 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 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 1996PhDT........63W) X-ray-selected source list
4771 = Wolk's (1996PhDT........63W 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 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 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 2003A&A...404..171B;
2 = Sacco et al. 2008, Cat. J/A+A/488/167;
3 = Zapatero Osorio et al. 2002A&A...384..937Z 2002A&A...384..937Z;
4 = Kenyon et al. 2005, Cat. J/MNRAS/356/89;
5 = Muzerolle et al. 2003ApJ...592..266M 2003ApJ...592..266M;
6 = Caballero et al. 2006A&A...445..143C 2006A&A...445..143C;
7 = Caballero et al. 2008A&A...491..515C 2008A&A...491..515C;
8 = Caballero et al. 2007A&A...470..903C 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 2009A&A...505.1115L;
13 = Hernandez et al. 2007, Cat. J/ApJ/662/1067;
14 = Luhman et al. 2008ApJ...688..362L 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 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 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 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 2004A&A...424..857C;
16 = Bailer-Jones & Mundt 2001A&A...367..218B 2001A&A...367..218B;
17 = Zapatero Osorio et al. 2003A&A...408..663Z 2003A&A...408..663Z.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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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
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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- 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)
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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.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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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)
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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 2008A&A...491..515C;
2 = Sacco et al. 2008, Cat. J/A+A/488/167;
3 = Zapatero Osorio et al. 2002A&A...384..937Z 2002A&A...384..937Z;
4 = Caballero et al. 2007A&A...470..903C 2007A&A...470..903C
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 19-Jan-2011