A HUBBLE SPACE TELESCOPE SURVEY OF H₂ EMISSION IN THE CIRCUMSTELLAR ENVIRONMENTS OF YOUNG STARS*

Abstract

The formation timescale and final architecture of exoplanetary systems are closely related to the properties of the molecular disks from which they form. Observations of the spatial distribution and lifetime of the molecular gas at planet-forming radii (a < 10 AU) are important for understanding the formation and evolution of exoplanetary systems. Toward this end, we present the largest spectrally resolved survey of H2 emission around low-mass pre-main-sequence stars compiled to date. We use a combination of new and archival far-ultraviolet spectra from the Cosmic Origins Spectrograph and Space Telescope Imaging Spectrograph instruments on the Hubble Space Telescope to sample 34 T Tauri stars (27 actively accreting Classical T Tauri Stars and 7 non-accreting Weak-lined T Tauri Stars) with ages ranging from ∼1 to 10 Myr. We observe fluorescent H2 emission, excited by Lyα photons, in 100% of the accreting sources, including all of the transitional disks in our sample (CS Cha, DM Tau, GM Aur, UX Tau A, LkCa 15, HD 135344B, and TW Hya). The spatial distribution of the emitting gas is inferred from spectrally resolved H2 line profiles. Some of the emitting gas is produced in outflowing material, but the majority of H2 emission appears to originate in a rotating disk. For the disk-dominated targets, the H2 emission originates predominately at a ≲ 3 AU. The emission line widths and inner molecular radii are found to be roughly consistent with those measured from mid-IR CO spectra.

The Muscles Treasury Survey. I. Motivation and Overview*

“…We measured the metal emission lines by employing a Gaussian line-fitting code that takes into account the linespread function of the instrument used to create that portion of the spectrum. For instance, the N Vand C IVlines are fit with a single-component Gaussian emission line convolved with the appropriate wavelength-dependent HST-COS line-spread function 21 (France et al 2012b). Some emission lines are clearly better described by a two-component model (Wood et al 1997), but this only applies to a small number of emission lines in the sample and we assume a single Gaussian for the results presented in this paper.…”

Violent environment of the inner disk of RW Aurigae A probed by the 2010 and 2015 dimming events

“…Our X-shooter data are taken well into the second dimming event. Since RW Aur A has been spectrally monitored at different wavelengths in the past decade, in particular in the optical (Alencar et al 2005;Chou et al 2013;Petrov et al 2015;Takami et al 2016) and in the UV (France et al 2012(France et al , 2014McJunkin et al 2013 The solid vertical lines show the dates when the UVES and X-shooter (black) spectra were taken (colour legend for UVES spectra is in Table 1). The dashed vertical lines show the dates of the four optical spectra by Chou et al (2013), which overlap on the used scale.…”

“…The dashed vertical lines show the dates of the four optical spectra by Chou et al (2013), which overlap on the used scale. The brown and grey dashed-dotted lines show the dates of the two UV HST spectra by France et al (2012France et al ( , 2014. Right panel: same as in left panel, zoomed during the second dimming event.…”

High-Resolution Ultraviolet Radiation Fields of Classical T Tauri Stars*

“…For N V, we load the 1237.1 -1243.9Å spectra into the multi-Gaussian fitting routine described in France et al (2012b) and fit all of the observed features with Gaussian emission lines convolved with the appropriate wavelength dependent HST +COS line-spread function (Kriss 2011) 11 . Emission lines with FWHM < 100 km s −1 and within ± 40 km s −1 of the rest wavelength of a known H 2 emission line pumped by Lyα [B -X (2 -2)R(11) λ1237.54Å, B -X (1 -2)P (8) λ1237.87Å, and C -X (1 -5)R(9) λ1240.87Å] were then subtracted from the data.…”