Embryonic Star Captured with Jets Flaring

[Dr. Spitzer]

More Spitzer news!

 

A developing star wrapped in a black cocoon of dust is seen sprouting giant jets in a new image from NASA's Spitzer Space Telescope.

 

The stellar portrait, captured in infrared light, offers the first glimpse at a very early stage in the life of an embryonic sun-like star -- a time when the star's natal envelope is beginning to flatten and collapse, and streams of gas are escaping. The observations will ultimately help astronomers better understand how stars and their planets form.

 

"This is the first time we've clearly seen a flattened envelope around a forming star," said Leslie Looney of the University of Illinois at Urbana-Champaign, lead author of a study about the star, called L1157, appearing Dec. 1 in Astrophysical Journal Letters. "Some theories had predicted that envelopes flatten as they collapse onto their stars and surrounding planet-forming disks, but we hadn't seen any strong evidence of this until now."

 

See the rest: http://www.spitzer.caltech.edu/Media/releases/ssc2007-19/release.shtml

[Martin]

thanks again, for another of these Caltech Spitzer telescope press releases.

this is a first.

 

the cloud surrounding the embryo star is flattening down into a disk, just as we always thought it did but hadn't actually seen it happen

 

AND some of the surplus gravitational energy is being got rid of by spurting jets out the N and S pole axis

 

AND the jets are not HOT like the million kelvin jets from an active galactic nucleus that we see a lot of pictures---and are much larger scale. these jets are just kind of LUKE WARM like a few hundred kelvin

 

At least that is what the press release says. It says 100 celsius. For me that is surprising. I always thought that ionization and magnetic field lines were involved in organizing jets. this gas seems too cold to be ionized

 

Would you like to give a rough idea of some possible mechanism these could form? Press release says pressure. What contains the pressure and why does it spurt out along the spin axis poles? Any intuition?

 

http://arxiv.org/abs/0711.4164

Morphological Evolution of Outflows from YSOs

Authors: Jonathan P. Seale, Leslie W. Looney

(Submitted on 27 Nov 2007)

 

Abstract: We present Spitzer IRAC images that indicate the presence of cavities cut into the dense outer envelope surrounding very young pre-main sequence stars. These young stellar objects (YSOs) characterized by an outflow represent the earliest stages of star formation. Mid-infrared photons thermally created by the central protostar/disk are scattered by dust particles within the outflow cavity itself into the line of sight. We observed this scattered light from 27 nearby, cavity-resolved YSOs, and quantified the shape of the outflow cavities. Using the grid models of Robitaille et al. (2006), we matched model spectral energy distributions (SEDs) to the observed SEDs of the 27 cataloged YSOs using photometry from IRAC, MIPS, and IRAS. This allows for the estimation of geometric and physical properties such as inclination angle, cavity density, and accretion rate. By using the relative parameter estimates determined by the models, we are able to deduce an evolutionary picture for outflows. Our work supports the concept that cavities widen with time, beginning as a thin jet-like outflow that widens to reveal the central protostar and disk until the protostellar envelope is completely dispersed by outflow and accretion.

 

Comments: Accepted to Astrophysical Journal

 

http://arxiv.org/abs/0710.2314

A Flattened Protostellar Envelope in Absorption around L1157

Authors: Leslie Looney, John Tobin, Woojin Kwon

(Submitted on 11 Oct 2007)

 

Abstract: Deep Spitzer IRAC images of L1157 reveal many of the details of the outflow and the circumstellar environment of this Class 0 protostar. In IRAC band 4, 8 microns, there is a flattened structure seen in absorption against the background emission. The structure is perpendicular to the outflow and is extended to a diameter of 2 arcminutes. This structure is the first clear detection of a flattened circumstellar envelope or pseudo-disk around a Class 0 protostar. Such a flattened morphology is an expected outcome for many collapse theories that include magnetic fields or rotation. We construct an extinction model for a power-law density profile, but we do not constrain the density power-law index.

 

Comments: ApJL accepted