TW Hya: SPECTRAL VARIABILITY, X-RAYS, AND ACCRETION DIAGNOSTICS

Journal Article · Tue May 01 04:00:00 EDT 2012 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/750/1/73· OSTI ID:22034555

Dupree, A K; Brickhouse, N S; Cranmer, S R; Luna, G J. M.; Schneider, E E ^[1]; Bessell, M S ^[2]; Bonanos, A ^[3]; Crause, L A ^[4]; Lawson, W A ^[5]; Mallik, S V ^[6]; Schuler, S C ^[7]

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1. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
2. Australian National Observatory, Mount Stromlo Observatory, Canberra, ACT 2611 (Australia)
3. Institute of Astronomy and Astrophysics, National Observatory of Athens, 15236 Athens (Greece)
4. South African Astronomical Observatory, P.O. Box 9, Observatory 7935, Cape Town (South Africa)
5. School of Physical, Environmental, and Math Sciences, University of New South Wales, Canberra, ACT 2600 (Australia)
6. Indian Institute of Astrophysics, Bangalore 560034 (India)
7. National Optical Astronomy Observatory, Tucson, AZ 85719 (United States)

The nearest accreting T Tauri star, TW Hya was intensively and continuously observed over {approx}17 days with spectroscopic and photometric measurements from four continents simultaneous with a long segmented exposure using the Chandra satellite. Contemporaneous optical photometry from WASP-S indicates a 4.74 day period was present during this time. The absence of a similar periodicity in the H{alpha} flux and the total X-ray flux which are dominated by accretion processes and the stellar corona, respectively, points to a different source of photometric variations. The H{alpha} emission line appears intrinsically broad and symmetric, and both the profile and its variability suggest an origin in the post-shock cooling region. An accretion event, signaled by soft X-rays, is traced spectroscopically for the first time through the optical emission line profiles. After the accretion event, downflowing turbulent material observed in the H{alpha} and H{beta} lines is followed by He I ({lambda}5876) broadening near the photosphere. Optical veiling resulting from the heated photosphere increases with a delay of {approx}2 hr after the X-ray accretion event. The response of the stellar coronal emission to an increase in the veiling follows {approx}2.4 hr later, giving direct evidence that the stellar corona is heated in part by accretion. Subsequently, the stellar wind becomes re-established. We suggest a model that incorporates the dynamics of this sequential series of events: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates determined from emission line profiles.

• OSTI ID: 22034555
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 750; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
ASTRONOMY
ASTROPHYSICS
COOLING
HEATING
HELIUM IONS
LINE BROADENING
MAIN SEQUENCE STARS
MASS
PERIODICITY
PHOTOMETRY
PHOTON EMISSION
PHOTOSPHERE
SOFT X RADIATION
STELLAR WINDS
T TAURI STARS
ULTRAVIOLET RADIATION