YSOVAR: The Young Stellar
Object Variability Project
Ann Marie Cody
Spitzer/IPAC, Caltech
YSOVAR: “WHY-SO-VARiable?”
Ann Marie Cody
Spitzer/IPAC, Caltech
Thanks to many collaborators…
John Stauffer (P.I.), Maria Morales-Calderón
At Caltech, JPL & LA: Luisa Rebull, Lynne
Hillenbrand, John Carpenter, Peter Plavchan,
Krzysztof Findeisen, Neal Turner, Susan
Terebey
And many other institutions:
The YSOVAR team: ysovar.ipac.caltech.edu
outline
 Motivation: Why do yet another photometric monitoring
campaign?
 What is YSOVAR?
 First results from YSOVAR
 A brief foray into NGC 2264
outline
 Motivation: Why do yet another photometric monitoring
campaign?
 What is YSOVAR?
 First results from YSOVAR
 A brief foray into NGC 2264
Hartmann 1999
Young stars are dynamic!
HH30:
HST/WFPC2 @
~1 frame per year
disk diameter ~ 450 AU
Light beam P~7.5d
(Duran-Rojas et al. 2009;
Watson & Stapelfeldt 2007)
We can learn about dynamics through time series
photometry
 80 days 
 80 days 
Periodic- Frasca
Stassunetetal.al.(2010)
1999
Aperiodic-
2003-2013:
A revolution in space based Monitoring of young stars
Spitzer
CoRoT
MOST
?
Optical
Alencar et al. (2010)
infrared
Morales-Calderón
et al. (2009)
outline
 Motivation: Why do yet another photometric monitoring
campaign?
 What is YSOVAR?
 First results from YSOVAR
 A brief foray into NGC 2264
Ysovar in a nutshell
 GO-6 Exploration Science program >500 hrs of Spitzer time
 Time series photometric monitoring at 3.6 and 4.5 um
 Includes ~1 square degree of the ONC plus 11 other wellknown SFRs
 Typically ~100 epochs/region (sampled ~2x/day for 40d, less
frequently at longer timescales)
 A couple thousand YSOs with good light curves!
 Data taken over the period Sep 2009 -- June 2011
Ysovar in a nutshell
Ysovar clusters
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
L1688
Serpens Main
Serpens South
IRAS 20050+2070
IC1396
Ceph-C
AFGL 490
NCG 1333
Orion
Mon R2
GGD 12-15
NGC 2264
Ysovar/Orion spitzer data
 ~250 hours of observing time
 ~ 1 square degree region of
the Orion Nebula cluster
Cadence: 40 days, with ∼2
epochs each day.
~1400 Class I and II Orion YSOs
with good quality time series (12% accuracy)
Ysovar/Orion Ground-based data
Near-IR:
• CFHT/WIRCAM: 10 nights. J & Ks
• UKIRT/WFCAM: ~30 epochs over 60 nights. J
• 2.1m KPNO/FLAMINGOS: 10 nights. JHKs
• CTIO 1.3/ANDICAM: ~30 epochs over 60 nights. J & I
• PAIRITEL: ~20 epochs over 35 nights. JHKs
• CAIN/TCS: 15 nights. J & Ks
Optical:
• USNO/Flagstaff: 7 nights. I band
• LOWELL/21”: 22 nights. I band
• NMSU-APO/40”: 24 nights. VI bands
• LCOGT/FTEM: 17 nights. I band.
• KPNO 24”/Slotis: 27 nights. I band
• CAHA 1.23m: 30 nights. BVI
• Arcsat APO, 0.5m: 5 nights. I band
Ysovar science goals
•Provide empirical constraints on physical processes and
structures characterizing the interaction between the star,
inner disk/envelope and accretion flows.
•Make unique measurements of the rotational periods of the
most embedded, youngest protostars
•Place constraints on the long-term variability of YSOs at IRAC
wavelengths.
•Discover new eclipsing binary systems to provide benchmarks
for young, low-mass evolution tracks
Light curve
acquisition
Morphological
classification
Search for correlations with
stellar/disk parameters
Comparison with
models
 Rotational evolution
 Disk structure
 Magnetospheric accretion
outline
 Motivation: Why do yet another photometric monitoring
campaign?
 What is YSOVAR?
 First results from YSOVAR
 A brief foray into NGC 2264
First results
An enormous variety
of light curves!
Ysovar/Orion Variability examples
Spitzer light curves: 3.6 and 4.5 μm
Morales-Calderón et al. (2011)
Ysovar/Orion Variability examples
Combined Spitzer and ground-based light curves
Morales-Calderón et al. (2011)
Ysovar/Orion Variability census
 70% of disk bearing stars are variable in the IRAC
bands
“Orion christmas
tree”
Light curve
acquisition
Morphological
classification
Search for correlations with
stellar/disk parameters
Comparison with
models
 Rotational evolution
 Disk structure
 Magnetospheric accretion
Periodic stars
• Can get a period for just 16% of the variable Class
I+IIs (90% of those are Class IIs, 10% are Class Is.)
 mostly seeing disks here
• For members w/o IR excess, 30% are variables,
mostly periodic  photosphere
• 30% of sample had literature period; 35% of those
are recovered, just 18% of those with IR excess
(thermal dust emission on top of stellar signal).
• 137 new periods.
Periodic stars
Tests of disk locking
YSOVAR: everything but Orion
YSOVAR: everything including Orion
Disk bearing
Bare photospheres
courtesy L. Rebull
6 new eclipsing binaries in orion
SpTs:
K0,K2
ISOY J05350447
P=3.906d
M1=0.83
M1=0.05
θ1 Ori E
M1=2.807
M2=2.797
SpTs:
M5,M6
Morales-Calderón et al. (2012)
“dippers”: Aa tau analogs
 41 examples in the Orion data.
 Flux dips ~0.1-0.4 mag IRAC
up to >1 mag at I and J
<3 days duration
 Usually one or two dips in 40 days
Extincting bodies?
Questions about dippers
• Disk must be seen at relatively high (and relatively narrow range of)
inclinations to do this, so expect that they are rare.
• YSOVAR Orion (year 1): Morales-Calderon et al. (2011) finds overall
fraction likely ~5% (2011).
• First CoRoT short run (2008) on NGC2264: Alencar et al. (2010) finds
overall fraction likely ~30%.
• What’s going on? Different ages of stars (Orion vs. NGC 2264)? Different
wavelengths (optical vs. IR)? Different cadences? (Different definitions of
the category?)
Large amplitude infrared behavior
 No variations at
shorter wavelengths.
Warped disks?
[4.5]
I
J
[3.6]
outline
 Motivation: Why do yet another photometric monitoring
campaign?
 What is YSOVAR?
 First results from YSOVAR
 A brief foray into NGC 2264
Ysovar’s successor:
the Coordinated Synoptic Investigation
of NGC 2264
 Spitzer: 30 days, 3.6-4.5 μm
 CoRoT: 40 days, optical
 Chandra/ACIS: 300ks (3.5 days)
 MOST: 40 days, optical
 VLT/Flames: ~20 epochs
 Ground-based monitoring
U-K bands: ~3 months
Magnitude [4.5]
CSI results: many pairs of optical and ir lightcurves
are uncorrelated!
CoRoT Spitzer
Magnitude [4.5]
Time (days)
CoRoT Spitzer
40 days
CSI results: optical/ir phase lags are rare
CoRoT Spitzer
Magnitude [4.5]
At least 10% of disk-bearing stars show
High-amplitude behavior in the ir only
Magnitude [4.5]
CoRoT Spitzer
Time (days)
High inclination:
Quasi-periodic flux dips caused by disk blobs or warps
Magnitude [4.5]
CoRoT Spitzer
Time (days)
Corot data reveals Flux events that may be accretion
bursts
 These objects have preferentially high UV excesses and
Hα emission indicative of strong accretion.
Light curve
acquisition
Periodic,
AA Tau
~11%
Disk-bearing stars
Periodic,
sinusoidal
~3%
Periodic, nonsinusoidal
~12%
Non-variable
optical/
variable IR
~10%
Aperiodic,
dipper
~13%
Aperiodic,
burster
~11%
Search for correlations with stellar/disk
parameters
Comparison with
models
Aperiodic,
stochastic
~26%
Nonvariable
~17%
An approach to classification
Flux Asymmetry
Bursters
Purely
periodic
Eclipsing
binaries
Quasi-periodic
stars
Stochastic
stars
Dippers
Stochasticity
classes can now be selected statistically!
Cody, Stauffer, in prep.
Summary and future plans
 We have performed a periodic variability census in the Orion dataset;
complete classification and understanding of aperiodic behavior remains
 Among the prominent variability types are “dippers” and high
amplitude infrared behavior…along with 6 new eclipsing binaries
 We find evidence for disk locking in all clusters
 We have just finished a complete morphological classification of
variability in NGC 2264 with CoRoT and Spitzer; we will now go back
to Orion and apply this framework
 Follow-up of interesting variables is upcoming; the long time baseline
available is another direction to pursue
 Stay tuned for further results from the full set of YSOVAR clusters
and the CSI project
First data release
You can download YSOVAR Orion data from:
http://ysovar.ipac.caltech.edu/first_data_release.html
http://cosmos.physast.uga.edu/Public/
Miscellaneous slides
Inner rim scale height changes
Ke et al. (2012)
60o
0.8 AU
V
J
3.6
No magnetic support
Neal Turner, JPL
60o
0.8 AU
V
J
3.6
Magnetic support near 0.1 AU
… Enter csi 2264
Magnitude [4.5]
CoRoT Spitzer
Time (days)
Magnitude [4.5]
CoRoT Spitzer
40 days
Fading events become deeper in the infrared
as we go to lower mass…
CoRoT Spitzer
disk-bearing stars:
Unexplained Periodic behavior
CoRoT Spitzer
Spitzer
Magnitude [4.5]
…And some objects are just plain bizarre!
Magnitude [4.5]
CoRoT Spitzer
Time (days)
Other possibilities for infrared variability mechanisms
 Disk scale height changes (due to x-ray ionization or
magnetic turbuluence)
 Heating by stellar hotspots, followed by dust sublimation
or IR re-emission
 Disk asymmetries (warps, overdensities) causing occultation
events or bright/dark spots
Need simultaneous monitoring at multiple
Wavelengths to assess these models
Magnitude
Corot data reveals Flux events that may be accretion
bursts
Time (days)
 These objects have preferentially high UV excesses and
Hα emission indicative of strong accretion.
Stauffer, Cody, in prep.
MOST enigmatic target: HD 31305
P=2.94 d
The combination of periodic variability plus stochastic residuals is highly
suggestive of a young star- but unheard of for such an early spectral type!
 A new type of young A star variability?
Cody et al. (2013)
Light curve
acquisition
Non-variable
Periodic
Aperiodic
Search for correlations with stellar/disk
parameters
Starspots
Disk
processes
su aurigae: mysterious periodicity observed with most
P=2.66 d
Cody & Hillenbrand (2013)
•Light curve behavior that appears periodic– but not perfectly
•Periodicity is too long to be consistent with the spectroscopic
rotation velocity, vsini  disk-related variability? P  0.05 AU
•Previous studies would not have separated this phenomenon
from stellar spot-dominated light curves
•Further evidence for periodic variability originating in disks
was recently published by Artemenko et al. (2013)
Light curve
acquisition
Non-variable
Periodic
Aperiodic
Search for correlations with stellar/disk
parameters
Starspots
Disk
processes