Papers by Georgina Beristain-Kendall
The Astrophysical Journal, 1998
We present a study of permitted emission lines of Fe I and Fe II in the spectrum of the highÈaccr... more We present a study of permitted emission lines of Fe I and Fe II in the spectrum of the highÈaccretion rate classical T Tauri star DR Tau. Echelle spectra collected at the 4 m Mayall telescope at Kitt Peak National Observatory between 1988 and 1992 include four epochs with red spectral coverage (D5000È 6800 and three with blue spectral coverage (D4000È4950 A total of 62 unblended Fe I and Fe II Ó) Ó). lines are identiÐed, their proÐles are examined, and ratios of line pairs that are sensitive to column density or temperature are analyzed. The unblended Fe proÐles exhibit a systematic behavior, with FWHM increasing from 20 to between 70 and 90 km s~1 as the equivalent width increases from 0.05 to several Two-component Ðts to the Ó. proÐles suggest a composite origin, comprising a narrow component (NC), with FWHM D 20 km s~1 and a radial velocity at rest with respect to the photosphere, and a broad component (BC), with FWHM D 100 km s~1 and a tendency to be blueshifted by ¹10 km s~1. These two kinematic components are present in di †ering proportions among lines of di †ering intensity, thereby accounting for the systematic behavior of the proÐles with line strength. Estimates of opacities and column densities are obtained by comparing observed intensity ratios of lines from a common upper level with values expected from a local escape probability calculation. We Ðnd that (1) opacities in the NC exceed those in the BC by factors of 2È4 and (2), for the BC, N Fe I Z 1017È1018 cm~2 and cm~2 for kinetic temperatures in the range 4000È10,000 K. N Fe II Z 1018È1019 Ratios of NC-to-BC emission from a pair of Fe I lines that are insensitive to opacity suggest that the kinetic temperature in the NC exceeds that in the BC by several thousand degrees. The centroid velocity and width of the NC in Fe I and Fe II are comparable to those from photospheric lines, suggesting a thermal or turbulent origin further broadened by stellar rotation. In the context of a magnetospheric accretion model, the NC is consistent with an origin in the postshock gas close to the stellar surface. In contrast, the BC is likely to be broadened by bulk motion, such as infalling gas in the accretion funnel or rotation in the region coupling the inner disk to the stellar magnetic Ðeld.
The Astrophysical Journal, 2001
High-resolution emission-line proÐles of He I and He II in 31 classical T Tauri stars are analyze... more High-resolution emission-line proÐles of He I and He II in 31 classical T Tauri stars are analyzed with the aim of probing the environs of the star-disk interface in accreting low-mass young stars. The diagnostic power of the helium lines lies in their high-excitation potentials, which restrict their formation to a region either of high temperature or close proximity to a source of ionizing radiation. The He I proÐles are decomposed into kinematic components that support the paradigm of magnetically controlled accretion from the disk onto the stellar surface but also require a signiÐcant contribution from a hot wind. A narrow component, seen in 28/31 stars, is characterized by relatively uniform line widths and centroid velocities among all the helium lines. Our analysis supports previous conclusions that this feature is consistent with formation in the decelerating postshock gas at the magnetosphere footpoint. A broad component, seen in 22/31 stars, displays a diversity of kinematic properties. Our analysis suggests that in many stars the He I broad component is itself composite. At one extreme are stars where the broad component is redshifted in excess of 8 km s~1, as would occur if helium emission arises primarily from polar angles less than in the funnel Ñow. At the other extreme are stars where the broad component 54¡ .7 is blueshifted in excess of [30 km s~1, requiring an origin in outÑowing gas. The additional occurrence of maximum blue wing velocities exceeding [200 km s~1 in 14 stars leads us to argue that hot winds are present in about half of our sample. The relation between the narrow component and the optical veiling di †ers between the stars with or without a hot helium wind, suggesting that when the hot wind is present the luminosity and temperature of the accretion shock are reduced. A comparison of broad component helium emission with standard outÑow indicators leads us to suggest that there are two sources of inner wind in T Tauri accretion disk systems : one a hot polar/coronal wind that prevails in stars with high veiling, and the other a more widespread cool disk wind that is likely launched at the magnetosphere/disk boundary.
Results are presented for the He emission in 31 CTTS from the Taurus-Auriga molecular cloud spann... more Results are presented for the He emission in 31 CTTS from the Taurus-Auriga molecular cloud spanning two orders of magnitude in the mass accretion rate, and for the Fe emission in DR Tau, based on a series of high resolution echelle spectra. The He lines admit a description in terms of a narrow component ( NC) and a broad component (BC). The NC has FWHM between 32-55 km/s and centroid velocities near zero km/s or moderately redshifted, consistent with an origin in the postshock region of the magnetospheric accretion model. The BC, with FWHM between 128 and 287 km/s and centroid velocities between -93 and +35 km/s, includes a wind and an accretion component; we argue the BC is predominantly formed in the wind. Estimates of the wind and accretion component equivalent widths are oppositely related to the NC, so the NC equivalent width increases with the accretion component but decreases as the wind component increases. The NC is undetectable where profiles appear dominated by the wind,...
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Papers by Georgina Beristain-Kendall