Potential Drivers of Mid-Infrared Variability in Young Stars: Testing Physical Models with Multiepoch Near-Infrared Spectra of YSOs in ρ Oph
Abstract
Recent studies have identified several young stellar objects (YSOs) which exhibit significant mid-infrared (mid-IR) variability. A wide range of physical mechanisms may be responsible for these variations, including changes in a YSO's accretion rate or in the extinction or emission from the inner disk. We have obtained and analyzed multiepoch near-infrared (NIR) spectra for five actively accreting YSOs in the ρ Oph star-forming region along with contemporaneous mid-IR light curves obtained as part of the YSOVAR Spitzer/IRAC survey. Four of the five YSOs exhibit mid-IR light curves with modest (∼0.2–0.4 mag) but statistically significant variations over our 40-day observation window. Measuring the strengths of prominent photospheric absorption lines and accretion sensitive H I and He I lines in each NIR spectrum, we derive estimates of each YSO's spectral type, effective temperature (T_eff), and H-band extinction (A_H), and analyze the time evolution of their NIR veiling (r_H and r_K) and mass accretion rates (Ṁ_acc). Defining a YSO's evolutionary stage such that heavily veiled, high accretion rate objects are less evolved than those with lower levels of veiling and ongoing accretion, we infer that GY 314 is the most evolved YSO in our sample, with GY 308 and GY 292 at progressively earlier evolutionary stages. Leveraging our multiepoch, multiwavelength dataset, we detect significant variations in mass accretion rates over timescales of days to weeks, but find that extinction levels in these YSOs remain relatively constant. We find no correlation between these YSO mid-IR light curves and time-resolved veiling or mass accretion rates, such that we are unable to link their mid-IR variability with physical processes localized near the inner edge of the circumstellar disk or within regions which are directly responsive to mass accretion. We do find, however, that redshifted He I λ10830 emission, where present in our spectra, shows both quantitative and qualitative temporal correlations with accretion-sensitive H I emission lines. Blueshifted He I absorption, on the other hand, does not demonstrate a similar correlation, although the time-averaged strength of this blueshifted absorption is correlated with the time-averaged accretion rate in our sample of YSOs.
Additional Information
© 2012 The University of Chicago Press on behalf of the Astronomical Society of the Pacific. Received 2012 March 28; accepted 2012 September 18; published 2012 October 22. The authors would like to thank W. Fischer, R. Kurosawa, S. Offner, A. Cody, and E. Chiang for useful conversations, K. Luhman for kindly sharing his spectral data, as well as the anonymous referee, whose valuable comments helped improve this manuscript. We also owe a debt of gratitude to Bill Golish, who helped us obtain our SpeX observations with remarkable efficiency. K.R.C. acknowledges support for this work from the Hubble Fellowship Program, provided by NASA through Hubble Fellowship grant HST-HF-51253.01-A awarded by the STScI, which is operated by the AURA, Inc., for NASA, under contract NAS 5-26555. C.M.F. acknowledges support from the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1144152. This work is based in part on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This research has made use of NASA's Astrophysics Data System Bibliographic Services, the SIMBAD database, operated at CDS, Strasbourg, France, the NASA/IPAC Extragalactic Database, operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration, and the VizieR database of astronomical catalogs (Ochsenbein et al. 2000). IRAF (Image Reduction and Analysis Facility) is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. The Two Micron All Sky Survey was a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (California Institute of Technology). The University of Massachusetts was responsible for the overall management of the project, the observing facilities and the data acquisition. The Infrared Processing and Analysis Center was responsible for data processing, data distribution and data archiving. Kevin R. Covey is Visiting Astronomer at the Infrared Telescope Facility, which is operated by the University of Hawaii under Cooperative Agreement no. NNX-08AE38A with the National Aeronautics and Space Administration, Science Mission Directorate, Planetary Astronomy Program.Attached Files
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Additional details
- Eprint ID
- 35858
- Resolver ID
- CaltechAUTHORS:20121206-130320807
- HST-HF-51253.01-A
- NASA
- DGE-1144152
- NSF Graduate Research Fellowship
- NAS 5-26555
- NASA
- Created
-
2012-12-06Created from EPrint's datestamp field
- Updated
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2021-11-09Created from EPrint's last_modified field
- Caltech groups
- Infrared Processing and Analysis Center (IPAC)