magnetic fields play an important role in creating, driving, and in the evolution of outflows and jets from protostars and accretion disks. on the other hand, the temperature profile of the accretion disks may also affect the structure of the magnetic field and outflows. in this paper, we use the self-similar method in cylindrical coordinates to investigate the effect of the temperature profile...

We present Spitzer Infrared Spectrograph spectra of 28 Class I protostars in the Taurus star-forming region. The 5 to 36 μm spectra reveal excess emission from the inner regions of the envelope and accretion disk surrounding these predecessors of low-mass stars, as well as absorption features due to silicates and ices. Together with shorterand longer-wavelength data from the literature, we cons...

Upcoming surveys with the Herschel Space Observatory will yield far-IR photometry of large samples of young stellar objects, which will require careful interpretation. We investigate the color and luminosity diagnostics based on Herschel broad-band filters to identify and discern the properties of low-mass protostars. We compute a grid of 2016 protostars in various physical congurations, presen...

xvii Chapter 1 Motivation 1 Chapter 2 Stellar evolution, Compact Stars, Accretion discs and X-ray binaries 3 2.1 Stellar evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1 Star Formation . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1.1 Protostars . . . . . . . . . . . . . . . . . . . . . . . 3 2.1.1.2 Stellar Mass limits . . . . . . . . . . . . . . . . . . 5 ...

The ASCA satellite has recently detected variable hard X-ray emission from two Class I protostars in the ρ Oph cloud, YLW15 (IRS43) and WL6, with a characteristic time scale ∼ 20h. In YLW15, the X-ray emission is in the form of quasi-periodic energetic flares, which we explain in terms of strong magnetic shearing and reconnection between the central star and the accretion disk. The flare modell...

We report on extremely high velocity molecular gas, up to −80 km s relative to the ambient medium, in the giant star-formation complex 30 Doradus in the Large Magellanic Cloud (LMC), as observed in new 22 GHz H2O 616 → 523 maser emission spectra obtained with the Mopra radio telescope. The masers may trace the velocities of protostars, and the observed morphology and kinematics indicate that cu...

We summarize here the observed properties of “infrared companions” to TTauri stars and argue that their observational properties are identical to those of Class I sources. They may therefore be embedded protostars in a much earlier evolutionary phase than TTauri stars, in which case these multiple systems are significantly non-coeval as opposed to the majority of young binary systems. They woul...

We present observations of NGC1333 from SCUBA-2 on JCMT, observed as a JCMT Gould Belt Survey pilot project during the shared risk campaign when the first of four arrays was installed at each of 450 and 850 microns. Temperature maps are derived from 450μm and 850μm ratios under the assumption of constant dust opacity spectral index β = 1.8. Temperatures indicate that the dust in the northern (I...

Some evolved stars in the pre-planetary nebula phase produce highly-collimated molecular outflows that resemble the accretion-driven jets and outflows from pre-main sequence stars. We show that IRAS 16342-3814 (the Water Fountain Nebula) is such an object and present K-band integral field spectroscopy revealing a fast (> 150 km s) bipolar H2 outflow. The H2 emission is shock excited and may ari...

We present Hubble Space Telescope NICMOS imaging of W3 IRS 5, a binary high-mass protostar. In addition to the two protostars, NICMOS images taken in the F222M and F160W filters show three new 2.22 μm sources with very red colors; these sources fall within a region 5600 AU in diameter, and are coincident with a ∼ 100 M⊙, dense molecular clump. Two additional point sources are found within 0.4 (...