The Far-Ultraviolet "Continuum" in Protoplanetary Disk Systems II: CO Fourth Positive Emission and Absorption

Дата и время публикации : 2011-04-04T20:01:05Z

Авторы публикации и институты :
Kevin France
Eric Schindhelm
Eric B. Burgh
Gregory J. Herczeg
Graham M. Harper
Alexander Brown
James C. Green
Jeffrey L. Linsky
Hao Yang
Hervé Abgrall
David R. Ardila
Edwin Bergin
Thomas Bethell
Joanna M. Brown
Nuria Calvet
Catherine Espaillat
Scott G. Gregory
Lynne A. Hillenbrand
Gaitee Hussain
Laura Ingleby
Christopher M. Johns-Krull
Evelyne Roueff
Jeff A. Valenti
Frederick M. Walter

Ссылка на журнал-издание: Ссылка на журнал-издание не найдена
Коментарии к cтатье: 12 pages, 7 figures, 3 tables. ApJ – accepted
Первичная категория: astro-ph.EP

Все категории : astro-ph.EP

Краткий обзор статьи: We exploit the high sensitivity and moderate spectral resolution of the $HST$-Cosmic Origins Spectrograph to detect far-ultraviolet spectral features of carbon monoxide (CO) present in the inner regions of protoplanetary disks for the first time. We present spectra of the classical T Tauri stars HN Tau, RECX-11, and V4046 Sgr, representative of a range of CO radiative processes. HN Tau shows CO bands in absorption against the accretion continuum. We measure a CO column density and rotational excitation temperature of N(CO) = 2 +/- 1 $times$ 10$^{17}$ cm$^{-2}$ and T_rot(CO) 500 +/- 200 K for the absorbing gas. We also detect CO A-X band emission in RECX-11 and V4046 Sgr, excited by ultraviolet line photons, predominantly HI LyA. All three objects show emission from CO bands at $lambda$ $>$ 1560 AA, which may be excited by a combination of UV photons and collisions with non-thermal electrons. In previous observations these emission processes were not accounted for due to blending with emission from the accretion shock, collisionally excited H$_{2}$, and photo-excited H2; all of which appeared as a "continuum" whose components could not be separated. The CO emission spectrum is strongly dependent upon the shape of the incident stellar LyA emission profile. We find CO parameters in the range: N(CO) 10$^{18-19}$ cm$^{-2}$, T_{rot}(CO) > 300 K for the LyA-pumped emission. We combine these results with recent work on photo- and collisionally-excited H$_{2}$ emission, concluding that the observations of ultraviolet-emitting CO and H2 are consistent with a common spatial origin. We suggest that the CO/H2 ratio in the inner disk is ~1, a transition between the much lower interstellar value and the higher value observed in solar system comets today, a result that will require future observational and theoretical study to confirm.

Category: Physics