J/AJ/157/85 The CIDA Variability Survey of Orion OB1. II. (Briceno+, 2019)
The CIDA Variability Survey of Orion OB1.
II. Demographics of the young, low-mass stellar populations.
Briceno C., Calvet N., Hernandez J., Vivas A.K., Mateu C., Downes J.J.,
Loerincs J., Perez-Blanco A., Berlind P., Espaillat C., Allen L.,
Hartmann L., Mateo M., Bailey III J.I.
<Astron. J., 157, 85 (2019)>
=2019AJ....157...85B 2019AJ....157...85B (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Stars, pre-main sequence ; Surveys ;
Stars, variable ; Equivalent widths ; Photometry, VRI ;
Photometry, infrared
Keywords: open clusters and associations: individual (Orion OB1 association) -
stars: formation - stars: pre-main sequence - surveys
Abstract:
We present results of our large-scale, optical, multi-epoch photometric
survey across ∼180 square degrees in the Orion OB1 association,
complemented with extensive follow-up spectroscopy. Our focus is mapping
and characterizing the off-cloud, low-mass, pre-main-sequence (PMS)
populations. We report 2062 K- and M-type confirmed T Tauri members;
59% are located in the OB1a subassociation, 27% in the OB1b subassociation,
and the remaining 14% in the A and B molecular clouds. We characterize
two new clusterings of T Tauri stars, the HD 35762 and HR 1833 groups,
both located in OB1a not far from the 25 Ori cluster. We also identify
two stellar overdensities in OB1b, containing 231 PMS stars, and find
that the OB1b region is composed of two populations at different distances,
possibly due to the OB1a subassociation overlapping with the front of OB1b.
A ∼2 deg wide halo of young stars surrounds the Orion Nebula Cluster,
corresponding in part to the low-mass populations of NGC 1977 and NGC 1980.
We use the strength of Hα in emission, combined with the IR excess
and optical variability, to define a new type of T Tauri star, the C/W
class, stars we propose may be nearing the end of their accretion phase,
in an evolutionary state between classical and weak-lined T Tauri stars.
The evolution of the ensemble-wide equivalent width of Li Iλ6707
indicates a Li depletion timescale of ∼8.5 Myr. Disk accretion declines
with an e-folding timescale of ∼2 Myr, consistent with previous studies.
Description:
The CVSO consists of multi-epoch optical quasi-simultaneous V-, R-, and
I-band observations across the entire Orion OB1 association, obtained
with the 8000x8000 pixel QUEST CCD Mosaic camera (Baltay et al.
2002PASP..114..780B 2002PASP..114..780B), installed on the 1 m aperture Jurgen Stock
Schmidt-type telescope at the National Astronomical Observatory of
Venezuela. The system is optimized to operate in drift-scan mode: the
telescope remains fixed at a given hour angle and declination, and
because of sidereal motion, stars move across the length of each CCD.
The CVSO comprises 337 drift scans, listed in Table 1, performed along
strips of R.A. centered at declinations -5°, -3°, -1°, +1°,
+3°, and +5°. We included observations obtained specifically
for our program, but also for other programs that had targeted the same
part of the sky with the QUEST camera (e.g., Rengstorf et al.
2004ApJ...606..741R 2004ApJ...606..741R; Vivas et al. 2004, J/AJ/127/1158; Downes et al.
2008AJ....136...51D 2008AJ....136...51D, 2014, J/MNRAS/444/1793). The 4.7 Tb data set
corresponds to ∼15000 hr of observations in the V, R, and I filters,
obtained over 190 nights between 1999 and 2008.
A total of 7796 candidates fainter than V∼16 were observed in our
combined multi-fiber spectrograph campaigns. Both Hectospec and Hydra have
a 1 deg diameter field of view, while Michigan/Magellan Fiber System (M2FS)
has a 29.5 arcmin diameter field. Hectospec has 300 fibers, each 1.5" on
the sky. Hydra with the Red Channel has 90 fibers, each with a projected
diameter of 2.0", and M2FS offers up to 256 fibers, 128 for each of its
twin Littrow spectrographs, each fiber with a projected diameter of 1.2"
on the sky. In Table 2, we show the full log of all the multi-fiber
spectrograph observations for Hydra, Hectospec, and the M2FS.
We classified 2062 candidates as confirmed low-mass, PMS stars of K-
and M-type, based on our low-resolution spectra (passed Hα, Li I
criterion). The properties of each T Tauri star (TTS) are provided in
Table 3.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 49 337 CVSO observing log
table2.dat 125 62 WIYN-Hydra and MMT-Hectospec observing log
table3.dat 326 2062 T Tauri stars in the CVSO
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See also:
II/36 : UBV and uvby-beta observations of Orion OB1 Association
(Warren+ 1977)
J/A+A/289/101 : Orion OB1 association. I. (Brown+, 1994)
J/ApJS/101/117 : UBVRIJHKLMNQ photometry in Taurus-Auriga (Kenyon+ 1995)
J/AJ/127/1158 : QUEST RR Lyrae Survey first catalog (Vivas+, 2004)
J/AJ/129/907 : New Ori OB1 members (Briceno+, 2005)
J/AJ/131/2959 : Candidate low-mass PMS in 25 Orionis group (McGehee+, 2006)
J/ApJ/646/297 : Spitzer obs. of pre-main-sequence stars (Rebull+, 2006)
J/ApJ/661/1119 : Spectroscopy in the 25 Ori group (Briceno+, 2007)
J/ApJ/671/1784 : Ori OB1 IRAC/MIPS observations (Hernandez+, 2007)
J/AJ/144/192 : Spitzer survey of Orion A and B. I. YSO catalog
(Megeath+, 2012)
J/A+A/572/A89 : Young stellar object candidates toward Orion
(Sanchez+, 2014)
J/MNRAS/444/1793 : 25 Ori group low-mass stars (Downes+, 2014)
J/AJ/152/198 : Periods of 4-10 Myr old T Tauri members of Orion OB1
(Karim+, 2016)
J/ApJ/818/59 : IN-SYNC. IV. YSOs in Orion A (Da Rio+, 2016)
J/A+A/608/A148 : Stellar populations towards Orion with Gaia DR1
(Zari+, 2017)
J/AJ/153/188 : Spectroscopy of the foreground population in Orion A
(Fang+, 2017)
J/AJ/154/14 : Low-mass stars in 25 Ori group and Orion OB1a
(Suarez+, 2017)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 10 A10 "date" Date Date of the observation
12- 14 I3 --- Num [300/809] Observation number
16- 19 F4.1 deg DEdeg Degree of central Declination of drift scan
observation (J2000)
21- 26 F6.2 deg RAdeg Degree of Right Ascension of the beginning of
drift scan observation (J2000)
28- 33 F6.2 deg RAdeg2 Degree of Right Ascension of the end of drift
scan observation (J2000)
35- 38 A4 --- Filt Filter(s) used
40- 47 A8 "h:m:s" HA Hour angle (1)
49 A1 --- HAs [0ENW-] Hour angle side
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Note (1): For the entire drift scan observation.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 A11 "date" Date Date of the observation
13- 21 A9 --- Inst Instrument used
23- 26 A4 --- Field Field identifier (1)
28- 29 I2 h RAh Center Hour of Right Ascension (J2000)
31- 32 I2 min RAm Center Minute of Right Ascension (J2000)
34- 38 F5.2 s RAs Center Second of Right Ascension (J2000)
40 A1 --- DE- Center Sign of the Declination (J2000)
41- 42 I2 deg DEd Center Degree of Declination (J2000)
44- 45 I2 arcmin DEm Center Arcminute of Declination (J2000)
47- 50 F4.1 arcsec DEs Center Arcsecond of Declination (J2000)
52- 65 A14 s Texp Exposure time
67- 69 I3 --- Nobj [24/277] Number of objects
71-105 A35 --- Note Additional note
107-125 A19 --- Bibcode Bibcode of the reference in Note
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Note (1): The letter "H" corresponds to the Hectospec fields, "W" to Hydra, and
"M" to the Michigan/Magellan Fiber System (M2FS) fields.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- CVSO The CVSO number
8- 11 I4 --- H07 [9/2386]? Source identification from
Hernandez et al. (2007, J/ApJ/671/1784),
[HCB2007] OB1a NNNN in Simbad
13- 72 A60 --- OName Other designation(s) from SIMBAD
74- 75 I2 h RAh Hour of Right Ascension (J2000)
77- 78 I2 min RAm Minute of Right Ascension (J2000)
80- 85 F6.3 s RAs Second of Right Ascension (J2000)
87 A1 --- DE- Sign of the Declination (J2000)
88- 89 I2 deg DEd Degree of Declination (J2000)
91- 92 I2 arcmin DEm Arcminute of Declination (J2000)
94- 99 F6.3 arcsec DEs Arcsecond of Declination (J2000)
101-104 A4 --- SpType Spectral type
106-113 F8.3 0.1nm EWHa [-400/0.81] Equivalent width of
Hα λ6563 (Å)
115-120 F6.3 0.1nm EWLiI [0/1.6]?=99 Equivalent width of
Li I λ6707 (Å)
122-126 F5.3 0.1nm EWNaI [0.088/4.452]? Equivalent width of
Na I λ8200 (Å)
128-129 A2 --- Type T Tauri classification type (1)
131-136 F6.3 mag Vmagmean [13.248/20.489]? V band robust mean magnitude
(2)
138-142 F5.3 mag e_Vmagmean [0.001/0.57]? 1σ error in Vmagmean
144-146 I3 --- o_Vmagmean [0/140] Number of measurements in Vmagmean
148-153 F6.3 mag Rcmagmean [13.218/19.697]? Cousins R band robust mean
magnitude (2)
155-159 F5.3 mag e_Rcmagmean [0/0.118]? 1σ error in Rcmagmean
161-163 I3 --- o_Rcmagmean [0/96] Number of measurements in Rcmagmean
165-170 F6.3 mag Icmagmean [11.83/18.811]? Cousins I band robust mean
magnitude (2)
172-176 F5.3 mag e_Icmagmean [0/0.365]? 1σ error in Icmagmean
178-180 I3 --- o_Icmagmean [0/152] Number of measurements in Icmagmean
182-186 F5.3 mag AmpV [0/3.582]? V-band peak-to-peak amplitude
188-192 F5.3 mag AmpRc [0/3.048]? Rc-band peak-to-peak amplitude
194-198 F5.3 mag AmpIc [0/2.457]? Ic-band peak-to-peak amplitude
200-204 F5.3 mag Vstd [0/1.034]? V-band standard deviation
206-210 F5.3 mag Rcstd [0/0.692]? Rc-band standard deviation
212-216 F5.3 mag Icstd [0/0.691]? Ic-band standard deviation
218-227 E10.3 --- Vprob [0/9]? χ2 probability of variability
in V
229-237 E9.3 --- Rcprob [0/9]? χ2 probability of variability
in Rc
239-247 E9.3 --- Icprob [0/9]? χ2 probability of variability
in Ic
249-254 F6.3 --- LVRc [-4.858/37.717]? Stetson variability index
for V and Rc magnitudes (2)
256-261 F6.3 --- LVIc [-3.038/65.035]? Stetson variability index
for V and Ic magnitudes (2)
263-268 F6.3 --- LRcIc [-4.114/45.403]? Stetson variability index
for Rc and Ic magnitudes (2)
270-275 F6.3 mag Jmag [8.77/17.009]? 2MASS J band magnitude
277-281 F5.3 mag e_Jmag [0.019/0.195]? 2MASS 1σ combined error
in Jmag
283-288 F6.3 mag Hmag [7.781/16.148]? 2MASS H band magnitude
290-294 F5.3 mag e_Hmag [0.02/0.234]? 2MASS 1σ combined error
in Hmag
296-301 F6.3 mag Ksmag [7.451/16.044]? 2MASS Ks band magnitude
303-307 F5.3 mag e_Ksmag [0.018/0.23]? 2MASS 1σ combined error
in Ksmag
309-312 I4 K Teff [0/5575] Effective temperature (3)
314-318 F5.3 mag Av [0/5.672] Extinction in V band (4)
320-326 A7 --- Loc Location within the Orion OB1 association
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Note (1): Classification as follows:
C = Classical T Tauri star;
W = Weak T Tauri star;
CW = C/W T Tauri star.
Note (2): Stetson (1996PASP..108..851S 1996PASP..108..851S).
Note (3): Derived from interpolating the spectral type in Table A5 of
Kenyon & Hartmann (1995, J/ApJS/101/117).
Note (4): For 86% of the sample, AV was derived from the V-Ic color. For an
additional 8% of stars which lacked an I-band measurement, we used the V-J
color. For the remainder of the stars, we used either the R-I, R-J or I-J
colors. We adopted the Cardelli et al. (1989ApJ...345..245C 1989ApJ...345..245C) extinction law,
and intrinsic colors from Kenyon & Hartmann (1995, J/ApJS/101/117).
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History:
From electronic version of the journal
References:
Briceno et al. Paper I. 2005AJ....129..907B 2005AJ....129..907B, Cat. J/AJ/129/907
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 24-May-2019