J/AJ/156/71 K2 Campaign 2: young disk-bearing stars in Sco & Oph (Cody+, 2018)
The many-faceted light curves of young disk-bearing stars in Upper Sco -- Oph
observed by K2 Campaign 2.
Cody A.M., Hillenbrand L.A.
<Astron. J., 156, 71 (2018)>
=2018AJ....156...71C 2018AJ....156...71C (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Molecular clouds ; YSOs ; Accretion ;
Spectral types ; Stars, variable
Keywords: accretion, accretion disks - circumstellar matter -
protoplanetary disks - stars : pre-main sequence -
stars: variables: T Tauri, Herbig Ae/Be - starspots
Abstract:
The K2 Mission has photometrically monitored thousands of stars at high
precision and cadence in a series of ∼80-day campaigns focused on sections
of the ecliptic plane. During its second campaign, K2 targeted over
1000 young stellar objects (YSOs) in the ∼1-3 Myr ρ Ophiuchus and
5-10 Myr Upper Scorpius regions. From this set, we have carefully vetted
photometry from WISE and Spitzer to identify those YSOs with infrared
excess indicative of primordial circumstellar disks. We present here
the resulting comprehensive sample of 288 young disk-bearing stars from
B through M spectral types and analysis of their associated K2 light
curves. Using statistics of periodicity and symmetry, we categorize each
light curve into eight different variability classes, notably including
"dippers" (fading events), "bursters" (brightening events), stochastic,
and quasi-periodic types. Nearly all (96%) of disk-bearing YSOs are
identified as variable at 30-minute cadence with the sub-1% precision
of K2. Combining our variability classifications with (circum)stellar
properties, we find that the bursters, stochastic sources, and the largest
amplitude quasi-periodic stars have larger infrared colors, and hence
stronger circumstellar disks. They also tend to have larger Hα
equivalent widths, indicative of higher accretion rates. The dippers,
on the other hand, cluster toward moderate infrared colors and low
Hα. Using resolved disk observations, we further find that the
latter favor high inclinations, except for a few notable exceptions with
close to face-on disks. These observations support the idea that YSO
time-domain properties are dependent on several factors, including
accretion rate and view angle.
Description:
We aimed to assemble and analyze as complete a set of light curves as
possible for young, low-mass disk-bearing stars among the K2 Campaign 2
targets. We initially selected objects submitted under programs GO2020,
GO2047, GO2052, GO2056, GO2063, and GO2085, all specifically targeting
Upper Scorpius and ρ Ophiuchus members or candidate members. We added
objects from programs GO2104, GO2051, GO2054, GO2069, GO2029, GO2106,
GO2089, GO2092, GO2049, GO2045, GO2107, GO2075, and GO2114 to our sample,
but only if their proper motions were suggestive of membership in the
Upper Sco region. This resulted in a set of 2072 potential young stars,
upon which we made further cuts based on WISE photometry. The set of
light curves considered in this work (Table 1) includes 340 young stars
with presumably primordial circumstellar disks, of which 288 are
considered to have suitably good-quality light curves for further analysis.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 95 340 Young inner disk-bearing stars in K2 Campaign 2
table2.dat 54 288 Variability properties of young disk-bearing stars
in K2 Campaign 2
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See also:
J/ApJ/688/377 : Low-mass objects in Upper Scorpius. II. (Slesnick+, 2008)
J/ApJ/705/1226 : Planet-bearing stars in Spitzer (Bryden+, 2009)
J/ApJ/724/835 : The Spitzer c2d survey of WTTSs. III. (Wahhaj+, 2010)
J/AJ/147/82 : Monitoring of disk-bearing stars in NGC 2264 (Cody+, 2014)
J/ApJS/211/3 : NIR photometry variability in ρ Oph (Parks+, 2014)
J/A+A/579/A66 : Accretion in ρ-Ophiucus (Manara+, 2015)
J/AJ/155/196 : Analysis of K2 LCs for members of USco & ρ Oph
(Rebull+, 2018)
J/AJ/156/75 : Circumstellar disks in the Upper Sco association
(Esplin+, 2018)
J/AJ/156/76 : New young stars and brown dwarfs in Upper Sco (Luhman+, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 I9 --- EPIC [202610930/210282534] EPIC catalog identifier
11- 27 A17 --- 2MASS 2MASS catalog identifier (JHHMMSSss+DDMMSSs)
29- 37 A9 --- SpType Spectral type
39 A1 --- n_SpType [a] Note on SpType (1)
41- 67 A27 --- Ref Reference
69- 87 A19 --- Bibcode Bibcode of the reference
89 A1 --- Blend [Y] Blend flag (2)
91- 93 A3 --- Region Region (Oph or Sco)
95 A1 --- Flag [BFY] Sample flag (3)
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Note (1): Note as follows:
a = For EPIC 203924502 we disregard the spectral type of B2V given by
Wahhaj et al. (2010, J/ApJ/724/835) for this source, as it is inconsistent
with all previously reported spectral types, as well as our own
examination of independent spectra. Comments in the paper suggest that a
nearby HII region contaminates Spitzer photometry, which implies possible
contamination in the optical spectrum as well if sky subtraction was not
handled properly.
Note (2): Blend flag as follows:
Y = A blend case where ground-based photometry indicates another star or stars
contaminating the K2 aperture.
Note (3): Sample flag as follows:
Y = Included in our ultimate sample of disk-bearing stars;
F = Too faint for K2 photometry, not retained in ultimate sample;
B = Too bright, not retained in ultimate sample.
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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- 9 I9 --- EPIC [202610930/210282534] EPIC catalog identifier
11- 27 A17 --- 2MASS 2MASS catalog identifier (JHHMMSSss+DDMMSSs)
29- 31 A3 --- VType Variability type (1)
33- 37 F5.3 --- Amp [0.001/2.41] Amplitude, in normalized flux units (2)
39- 43 F5.2 d Time [0.28/95.25] Variability timescale (3)
45- 48 F4.2 --- Q [0.02/1.01] Quasi-periodicity (4)
50- 54 F5.2 --- M [-1.35/1.24] Flux asymmetry (5)
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Note (1): Variability types are determined by eye and supported by statistical
measures. The types consist of the following:
P = Strictly periodic behavior;
MP = Stars with multiple distinct periods;
QPD = Quasi-periodic dippers;
QPS = Quasi-periodic symmetric (i.e., quasi-periodic stars that neither burst
nor dip);
APD = Aperiodic dippers;
B = Bursters;
S = Stochastic stars;
L = Long-timescale behavior that does not fall into the other categories;
U = Objects we were unable to classify;
N = Non-variable objects;
QP = Quasi-periodic objects.
Note (2): Amplitudes are measured by determining the normalized flux difference
between the 95th and 5th percentile points in the light curve; this is
similar to a peak-to-peak amplitude, but is less sensitive to outliers and
other errant points.
Note (3): The variability timescale is defined as the period from periodogram
analysis, if Q<0.8 (i.e., the light curve is [quasi-]periodic). For stars with
Q>0.8, a timescale is derived in the same manner as described in Cody et al.
(2014, J/AJ/147/82, see Section 6.5).
Note (4): The ratio of the residual variance to the original light curve
variance. It measures on a scale of 0 to 1 how periodic (0) or stochastic (1)
the light curve is. Light curves with low residual noise after removal of the
phased pattern are then highly periodic (Q∼0), whereas those that have larger
residuals are quasi-periodic or aperiodic.
Note (5): The measure of the tendency of a light curve to display fading events
(positive M) or brightening events (negative M), or a more symmetric,
non-skewed light curve that is perhaps a mixture of the two (M∼0). The value
of M is determined by calculating a "mean" flux value (by averaging the bottom
and top 95th percentile points), subtracting off the median flux value, and
then dividing by the estimated white noise level.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 05-Feb-2019