J/AJ/155/99 IR variability among YSOs in the Serpens South cluster (Wolk+, 2018)
YSOVAR: mid-infrared variability among YSOs in the star formation region
Serpens South.
Wolk S.J., Gunther H.M., Poppenhaeger K., Winston E., Rebull L.M.,
Stauffer J.R., Gutermuth R.A., Cody A.M., Hillenbrand L.A., Plavchan P.,
Covey K.R., Song I.
<Astron. J., 155, 99 (2018)>
=2018AJ....155...99W 2018AJ....155...99W (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Star Forming Region ; YSOs ;
Photometry, infrared ; Stars, variable
Keywords: accretion, accretion disks - infrared: stars - stars: formation -
stars: pre-main sequence - stars: protostars
Abstract:
We present a time-variability study of young stellar objects (YSOs) in
the Serpens South cluster performed at 3.6 and 4.5 µm with the
Spitzer Space Telescope; this study is part of the Young Stellar
Object VARiability project. We have collected light curves for more
than 1500 sources, including 85 cluster members, over 38 days. This
includes 44 class I sources, 19 sources with flat spectral energy
distributions (SEDs), 17 class II sources, and five diskless YSO
candidates. We find a high variability fraction among embedded cluster
members of ∼70%, whereas young stars without a detectable disk display
no variability. We detect periodic variability for 32 sources with
periods primarily in the range of 0.2-14 days and a subset of fast
rotators thought to be field binaries. The timescale for brightness
changes are shortest for stars with the most photospheric SEDs and
longest for those with flat or rising SEDs. While most variable YSOs
become redder when fainter, as would be expected from variable
extinction, about 10% get bluer as they get fainter. One source,
SSTYSV J183006.13-020108.0, exhibits "cyclical" color changes.
Description:
For this program, the field was observed using Spitzer from 2011 May
through June (starting on about MJD 55700); these data are referred to
as Young Stellar Object VARiability project (YSOVAR) data. The YSOVAR
data were generated by a pair of pointings (one for [3.6] and one for
[4.5]) with a field center of 18:30:04-02:02:05 (J2000; see Figure 1
and Rebull et al. 2014AJ....148...92R 2014AJ....148...92R (Paper I); Figure 35). A fast
cadence was used, meaning the observations were made in a series of
3.5 day cycles. Within each cycle, the time step between visits was
incremented in 2 hr intervals from 4 to 16 hr. By using a linearly
increasing time step, we were able to evenly sample, in Fourier space,
a range of higher frequency (shorter timescale) photometric variability
while minimizing the total amount of observing time necessary to sample
these high frequencies and to minimize the period aliasing (see Paper I).
The YSOVAR data consist of 82 observations of Serpens South over a 38 day
period with a total exposure time of 14.7 hr.
Objects:
------------------------------------------------------------------------
RA (ICRS) DE Designation(s)
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18 30 03.00 -02 01 58.2 Serpens South = NAME Serpens South Cluster
------------------------------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 148 303 *Source designations, flux densities and
lightcurve properties of sources rejected
table2.dat 296 1524 Source designations, flux densities and
lightcurve properties of the sources used in
this study
table3.dat 75 32 Properties of periodic sources
table6.dat 70 8 Properties of the eight stars with Stetson
index > 5
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Note on table1.dat: Sources were rejected from further analysis for being
relatively faint and hence not included in the cryo analysis.
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See also:
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
J/A+A/421/623 : ISOCAM survey of YSOs in Serpens Cloud Core (Kaas+, 2004)
J/A+A/463/275 : Chandra obs. of Serpens star-forming region (Giardino+, 2007)
J/ApJ/663/1149 : Spitzer survey of Serpens YSO population (Harvey+, 2007)
J/ApJ/669/493 : Spitzer/Chandra YSOs in Serpens cloud core (Winston+, 2007)
J/ApJ/691/672 : Spectrocopy of YSOs in Serpens molecular cloud
(Oliveira+ 2009)
J/ApJ/692/973 : Protostars in Perseus, Serpens and Ophiuchus (Enoch+, 2009)
J/ApJS/184/18 : Spitzer survey of young stellar clusters (Gutermuth+, 2009)
J/ApJ/714/778 : YSOs in the Serpens Molecular Cloud (Oliveira+, 2010)
J/AJ/149/103 : Spectroscopy of candidate YSOs in Serpens (Erickson+, 2015)
J/A+A/615/A9 : Distribution of Serpens South protostars (Plunkett+, 2018)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000)
13- 24 F12.9 deg DEdeg Declination in decimal degrees (J2000)
26- 51 A26 --- IAU IAU designation within YSOVAR program
(SSTYSV JHHMMSS.ss DDMMSS.s)
53- 64 A12 --- UKIDSS UKIDSS designation
66- 71 F6.3 mag Kmag [14.437/18.916]? UKIDSS K band 1" aperture
magnitude
73- 77 F5.3 mag e_Kmag [0.007/0.335]? Statistical error in Kmag
79- 81 A3 --- SClass [F I II III] IR class according to SED slope
(G1)
83- 84 I2 --- o_3.6mag [0/82] Number of data point(s) in 3.6mag
86- 87 I2 --- o_4.5mag [0/82] Number of data point(s) in 4.5mag
89- 93 F5.2 mag 3.6mag [12.29/16.33]? Median Spitzer/IRAC 3.6 micron
band magnitude
95- 99 F5.2 mag 4.5mag [10.88/15.99]? Median Spitzer/IRAC 4.5 micron
band magnitude
101-105 F5.2 mag 3.6magmean [12.29/16.34]? Mean Spitzer/IRAC 3.6 micron
band magnitude
107-111 F5.2 mag 4.5magmean [10.88/15.97]? Mean Spitzer/IRAC 4.5 micron
band magnitude
113-116 F4.2 mag Delta3.6 [0.07/0.93]? Distribution width from 10-90%
in 3.6mag
118-121 F4.2 mag Delta4.5 [0.04/0.94]? Distribution width from 10-90%
in 4.5mag
123-127 F5.2 --- Stetson [-0.96/4.07]? Stetson index for 3.6 and
4.5 micron band lightcurve
129-134 F6.2 --- chi2(3.6) [0.18/846.3]? Reduced χ2 to mean
in 3.6mag
136-140 F5.2 --- chi2(4.5) [0.06/59.67]? Reduced χ2 to mean
in 4.5mag
142-144 F3.1 d CTime3.6 [0.3/9.5]? Decay time of autocorrelation
function (ACF) in 3.6mag
146-148 F3.1 d CTime4.5 [0.4/9.9]? Decay time of ACF in 4.5mag
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000)
13- 24 F12.9 deg DEdeg Declination in decimal degrees (J2000)
26- 51 A26 --- IAU IAU designation within YSOVAR program
(SSTYSV JHHMMSS.ss DDMMSS.s)
53- 56 I4 --- CClass [-100/99]? IR class according to color cuts
(G3)
58- 60 A3 --- SClass [F I II III] IR class according to SED slope
(G1)
62- 66 A5 --- SSet [TRUE FALSE] Source is in YSOVAR standard set
(G2)
68- 72 A5 --- ASet [TRUE FALSE] Source is in YSOVAR augmented
set (1)
74- 78 A5 --- Var [TRUE FALSE] Source is variable
80- 84 A5 --- X-ray [TRUE FALSE] An X-ray source
86- 88 I3 --- o_3.6mag [0/104] Number of data point(s) in 3.6mag
90- 91 I2 --- o_4.5mag [0/85] Number of data point(s) in 4.5mag
93- 97 F5.2 mag 3.6mag [7.43/16.58]? Median Spitzer/IRAC 3.6 micron
band magnitude
99-103 F5.2 mag 4.5mag [6.26/16]? Median Spitzer/IRAC 4.5 micron
band magnitude
105-109 F5.2 mag 3.6magmean [7.41/16.53]? Mean Spitzer/IRAC 3.6 micron
band magnitude
111-115 F5.2 mag 4.5magmean [6.25/16]? Mean Spitzer/IRAC 4.5 micron band
magnitude
117-120 F4.2 mag Delta3.6 [0.02/0.54]? Distribution width from 10-90%
in 3.6mag
122-125 F4.2 mag Delta4.5 [0.01/0.62]? Distribution width from 10-90%
in 4.5mag
127-131 F5.2 --- Stetson [-0.46/15.54]? Stetson index for 3.6 and
4.5 micron band lightcurve
133-138 F6.2 --- chi2(3.6) [0.09/269.86]? Reduced χ2 to mean
in 3.6mag
140-145 F6.2 --- chi2(4.5) [0.1/569.88]? Reduced χ2 to mean
in 4.5mag
147-151 F5.2 d Per [0.12/13.98]? Period
153-155 F3.1 d CTime3.6 [0.2/9.2]? Decay time of autocorrelation
function (ACF) in 3.6mag
157-159 F3.1 d CTime4.5 [0.2/9.5]? Decay time of ACF in 4.5mag
161-164 F4.2 mag CMDLength [0/0.75]? Length of fitted color-magnitude
diagram (CMD) vector (2)
166-170 F5.1 deg CMDAngle [1.8/169.1]? Fitted CMD slope angle (2)
172-175 F4.1 deg e_CMDAngle [0.4/90]? The 1σ error in CMDAngle
177-182 F6.3 mag Jmag [10.553/17.288]? 2MASS J band magnitude
184-187 F4.2 mag e_Jmag [0.02/0.33]? Statistical error in Jmag
189-194 F6.3 mag Hmag [8.256/16.44]? 2MASS H band magnitude
196-199 F4.2 mag e_Hmag [0.02/0.26]? Statistical error in Hmag
201-206 F6.3 mag Ksmag [7.193/15.403]? 2MASS Ks band magnitude
208-211 F4.2 mag e_Ksmag [0.02/0.2]? Statistical error in Ksmag
213-217 F5.2 mag 3.6magC [6.54/17.75]? Cryogenic Spitzer/IRAC
3.6 micron band magnitude
219-222 F4.2 mag e_3.6magC [0/0.49]? Statistical error in 3.6magC
224-228 F5.2 mag 4.5magC [6.41/16.65]? Cryogenic Spitzer/IRAC
4.5 micron band magnitude
230-233 F4.2 mag e_4.5magC [0/0.28]? Statistical error in 4.5magC
235-239 F5.2 mag 5.8magC [5.51/15.74]? Cryogenic Spitzer/IRAC
5.8 micron band magnitude
241-244 F4.2 mag e_5.8magC [0/0.5]? Statistical error in 5.8magC
246-250 F5.2 mag 8.0magC [4.28/14.68]? Cryogenic Spitzer/IRAC
8.0 micron band magnitude
252-255 F4.2 mag e_8.0magC [0/0.73]? Statistical error in 8.0magC
257-260 F4.2 mag 24magC [0.59/9.88]? Cryogenic Spitzer/MIPS 24 micron
band magnitude
262-265 F4.2 mag e_24magC [0/0.3]? Statistical error in 24magC
267-270 F4.2 mag AK [0/6.86] Extinction in K band
272-277 F6.3 mag Kmag [10.108/18.668]? UKIDSS K band 1" aperture
magnitude
279-283 F5.3 mag e_Kmag [0/0.241]? Statistical error in Kmag
285-296 A12 --- UKIDSS UKIDSS designation
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Note (1): The "augmented set" is composed of X-ray sources that are brighter
than 15 mag in either [3.6] or [4.5] and that have SED slopes consistent with
class I, F, or II objects, but the colors of these objects are not sufficient
for positive identification as YSOs.
Note (2): 3.6 and 4.5 micron band.
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Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 A18 --- IAU IAU designation within YSOVAR program
(SSTYSV JHHMMSS.ss DDMMSS.s)
20- 22 A3 --- Xray [Yes No] An Xray source?
24- 26 A3 --- SSet [Yes No] Part of the standard set of cluster
members? (G2)
28- 32 F5.2 d Per [0.12/13.98] Period
34- 37 F4.2 d e_Per [0/1.02]? Uncertainty in Per
39- 43 F5.3 --- FAP [0/0.061] False alarm probability
45- 49 F5.2 --- Power [11.49/25.9] Power of the periodogram peak
51- 54 I4 --- GClass [-100/99] Color class from Gutermuth et al.
(2009, J/ApJS/184/18) (G3)
56- 58 A3 --- SClass [F I II III] The 2-24 µm SED slope class (G1)
60- 64 A5 --- Filt1 First filter/color ([3.6]-[4.5]) used (1)
65 A1 --- n_Filt1 [p] Note on Filt1 (p=Filter used for the period
value) (1)
67- 68 I2 --- Filt2 [45]? Second filter used (1)
69 A1 --- n_Filt2 [p] Note on Filt2 (p=Filter used for the period
value) (1)
71- 75 A5 --- Filt3 Third color ([3.6]-[4.5]) used (1)
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Note (1): In priority order, we take any period derived from the [3.6] data
first ([3.6] is less noisy than [4.5]); then, only if there is no [3.6] period
of sufficient power, we take the period derived from [4.5]. We also derived a
period from the [3.6]-[4.5] color.
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Byte-by-byte Description of file: table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 26 A26 --- IAU IAU designation within YSOVAR program
(SSTYSV JHHMMSS.ss DDMMSS.s)
28 I1 --- CClass [1/2] IR class according to color cuts
30- 31 A2 --- SClass [F I II] IR class according to SED slope (G1)
33- 37 F5.2 mag 3.6mag [7.43/13.73] Median Spitzer/IRAC 3.6 micron
band magnitude
39- 42 F4.2 mag e_3.6mag [0.18/0.54] Uncertainty in 3.6mag
44- 48 F5.2 mag 4.5mag [6.26/12.17] Median Spitzer/IRAC 4.5 micron
band magnitude
50- 53 F4.2 mag e_4.5mag [0.18/0.48] Uncertainty in 4.5mag
55- 59 F5.2 --- Stetson [5.42/15.54] Stetson index for 3.6 and
4.5 micron band lightcurve
61- 65 F5.2 deg CMDAngle [75.54/95.99] Fitted color-magnitude diagram
(CMD) slope angle
67- 70 F4.2 deg e_CMDAngle [0.43/4.18] Uncertainty in CMDAngle
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Global notes:
Note (G1): Spectral index code defined as follows:
I = Class I source with a spectral slope α>0.3;
F = Flat-spectrum source with 0.3<α←0.3;
II = Class II source with 1.6<α←0.3;
III = Class III source with α←1.6, typically assumed to have no disk.
Class III, class II, and class I objects range from no to moderate X-ray
variability. This is discussed in more detail by E. Winston et al.
(2018AJ....155..241W 2018AJ....155..241W).
Note (G2): The "standard set" is defined as the union of color-classed YSOs and
X-ray sources with α>-1.6.
Note (G3): Class as follows:
99 = Disk-free;
-100 = Unknown.
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History:
From electronic version of the journal
References:
Rebull et al. Paper I. 2014AJ....148...92R 2014AJ....148...92R
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 23-Oct-2018