LkHα 101 at millimeter wavelengths

Abstract

We present new millimeter observations made with the IRAM interferometer and 30 m telescope of the ionized wind from the massive young stellar object LkHα 101. Several recombination lines, including higher order transitions, were detected for the first time at radio wavelengths in this source. From three α-transitions, we derive an accurate value for the stellar velocity and for the first time, an unambiguous expansion velocity of the wind that is 55 km s −1 . This velocity is much slower than reported previously, and the resulting mass loss rate is 1.8 × 10 −6 M yr −1 . The wideband continuum spectra and the interferometer visibilities show that the density of the wind falls off more steeply than what is compatible with constant-velocity expansion. We argue that these properties indicate that the wind is launched from a radially narrow region of the circumstellar disk, and we propose that slow speed and a steep density gradient are characteristic properties of the evolutionary phase, where young stars of intermediate and high mass clear away the gaseous component of their accretion disks. The recombination lines are emitted close to local thermal equilibrium, but the higher order transitions appear systematically broader and weaker than expected, probably because of impact broadening. Finally, we show that LkHα 101 shares many properties with MWC 349, the only other stellar wind source where radio recombination lines have been detected, with some of them masing. We argue that LkHα 101 evades masing at millimeter wavelengths because of the disk's smaller size and unfavorable orientation. Some amplification may however be detectable at shorter wavelengths.

Radio jets from young stellar objects

“…Jiménez-Serra et al (2013) propose that the radio recombination lines arise from a dense and collimated jet embedded in a cylindrical ionized wind, oriented nearly along the line of sight. In the case of LkHα101, Thum et al (2013) find the millimeter RRLs to be close to LTE and to show non-Gaussian wings that can be used to infer the velocity of the wind, in this case 55 km s −1 . Finally, Guzmán et al (2014) detect millimeter recombination lines from the high-mass young stellar object G345.4938+01.4677.…”

VLBA Determination of the Distance to Nearby Star-forming Regions. VIII. The LkHα 101 Cluster

“…It illuminates the reflection nebula NGC 1579 and has a directly imaged disk (see the review by Andrews & Wolk 2008, and references therein). It also hosts a small HII region that is sustained by the ionized winds from its disk (Thum et al 2013). LkHα 101 is associated with a cluster of young low-mass stars (hereafter, the LkHα 101 cluster), some of which are magnetically active (Becker & White 1988;Stine & O'Neal 1998;Osten & Wolk 2009).…”

Submillimetre free–free emission from the winds of massive stars in the age of Atacama Large Millimeter/submillimeter Array

“…The treatment of other velocity laws than equation ( 6) is however, beyond the scope of this study. Thum et al (2013) present millimeter observations of the massive stellar object LkHα101. By analysing highn line transitions they deduce a slow moving wind whose spectral flux corresponds to a non-constant wind velocity.…”

“…Due to a mixture of differing physical regimes within the stellar atmosphere close to the base of the wind, the wind acceleration region is a challenging subject which until recently has received little treatment both theoretically and observationally. This situation is changing due to ALMA and the wind acceleration region has begun to receive attention for example in the context of pre-main sequence stars (see Thum et al 2013).…”