Dissection of the protostellar envelope surrounding IRAS 05173-0555 in L1634

Astronomy and Astrophysics (Impact Factor: 4.38). 03/2008; 485(2). DOI: 10.1051/0004-6361:20079224
Source: arXiv


Context. The youngest protostars that power energetic outflows are surrounded by infalling and rotating envelopes that contain most of the mass of the system. Aims. To study the properties and kinematics of the protostellar envelope surrounding the embedded source IRAS 05173-0555 in L1634. Methods. We carried out VLA ammonia observations at 1.3 cm with the VLA in the D configuration to map the gas towards the core of L1634. Results. The NH3 emission towards IRAS 05173-0555 is resolved and shows two components clearly distinguishable morphologically: a cross-like structure, roughly elongated in the direction of the HH 240/241 outflow and associated with IRAS 05173-0555, plus an arc-like stream elongated towards the north. The properties and kinematics of the gas suggest that the origin of the cross-like morphology could be the interaction between the outflow and the envelope. A more compact and flattened structure, which could be undergoing rotation about the axis of the outflow, has been detected towards the center of the cross-like envelope. The northern stream, which has properties and velocity different from those of the cross-like envelope, is likely part of the original cloud envelope, and could be either a quiescent core that would never form stars, or be in a prestellar phase. Comment: 10 pages, 9 figures, accepted for publication in A&A

Download full-text


Available from: Alwyn Wootten, Sep 03, 2013
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: New observations of protostellar outflows associated with young stars in two of Orion's outlying cometary clouds, L1622 and L1634, are presented. The Hα surface brightness of the bright rims are used to argue that both clouds are located at a distance of about 400 pc in the interior of the Orion superbubble where they are illuminated by Orion's massive stars. Spitzer IRAC and MIPS images reveal 28 candidate young stellar objects (YSOs). Combined with the 14 spectroscopically confirmed T Tauri stars, there are at least 34 YSOs in L1622. Narrow-band images have led to the identification of about a dozen shock complexes in L1622. At least six belong to a highly collimated externally irradiated, bipolar jet, HH 963, that is powered by a low-luminosity Class II YSO located outside the projected edge of the L1622 dark cloud. However, the sources of most shocks remain unclear. The Spitzer/IRAC images reveal a compact, highly obscured, S-symmetric outflow brightest in the 4.5 μm images. A faint [S II] counter part, HH 962, is associated with the western end of this flow which appears to be powered by an obscured source in the L1622 cloud interior. The currently identified sample of YSOs implies a star formation efficiency of about 4% for L1622. The L1634 cloud contains nine YSOs and three outflows, including the well known HH 240/241 system. A new flow, HH 979, is powered by the embedded YSO IRS7 in L1634 and crosses the eastern lobe of the HH 240 outflow. Spitzer/IRAC images show 4.5 μm emission indicating molecular shocks from the Herbig-Haro objects closest to IRS 7. A YSO embedded in a condensation located 5' north of HH 240/241 is identified in the Spitzer images. This source drives an irradiated outflow, HH 980, whose lobes emerge into the ionized environment of the Orion-Eridanus superbubble interior. The star formation efficiency of L1634 is estimated to be about 3%.
    The Astronomical Journal 03/2009; 137(4):3843. DOI:10.1088/0004-6256/137/4/3843 · 4.02 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Bright-rimmed clouds (BRCs) appear to be sites of triggered star formation induced through the propagation of shocks initiated by the expansion of nearby H ii regions. Our main aim is to establish support for observations of star-forming activity within a sample of BRCs. A secondary aim is to establish a plausible link between such star formation and observed external influences. We have conducted CO (J = 2–1) observations using the James Clerk Maxwell Telescope to probe the environments of a sample of star-forming BRCs associated with embedded protostellar cores. Local thermodynamic equilibrium analysis allows the determination of the physical properties of these protostars and investigation of the structure and kinematic motions within the molecular gas. Using a combination of archival radio and mid-infrared data, and submillimeter observations, we have refined the Sugitani, Fukui and Ogura (SFO) catalogue, excluding 18 BRCs that do not show any evidence of photoionization induced collapse. Of the remaining 26 clouds that are being photoionized, we find 20 that are associated with embedded protostars. These 20 clouds are excellent candidates with which to further investigate the radiatively driven implosion mode of triggered star formation. Comparing the physical parameters of the triggered and untriggered samples, we find that the surface temperatures of the potentially triggered clouds are significantly higher (by ∼10 K) than those in which triggering is considered unlikely. The higher surface temperatures found towards the sample of potentially triggered clouds are consistent with the hypothesis that these clouds are being externally heated through their exposure to the H ii region.
    Monthly Notices of the Royal Astronomical Society 10/2009; 400(4):1726 - 1733. DOI:10.1111/j.1365-2966.2009.15585.x · 5.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cha-MMS1 was mapped in the NH_3(1,1) line and the 1.2 cm continuum using the Australia Telescope Compact Array, ATCA. The angular resolution of the ATCA observations is 7'' (~ 1000 AU), and the velocity resolution is 50 m s^{-1}. The core was also mapped with the 64-m Parkes telesope in the NH_3(1,1) and (2,2) lines. Observations from Herschel Space Observatory and Spitzer Space telescope were used to help interpretation. A compact high column density core with a steep velocity gradient is detected in ammonia, with a fractional ammonia abundance compatible with determinations towards other dense cores. The direction of the velocity gradient agrees with previous single-dish observations, and the overall velocity distribution can be interpreted as rotation. The rotation axis goes through the position of a compact far-infrared source detected by Spitzer and Herschel. The specific angular momentum of the core is typical for protostellar envelopes. A string of 1.2 cm continuum sources is tentatively detected near the rotation axis. The ammonia spectra suggest the presence of warm embedded gas in its vicinity. An hourglass-shaped structure is seen in ammonia at the cloud's average LSR velocity, also aligned with the rotation axis. Although this structure resembles a pair of outflow lobes the ammonia spectra show no indications of shocked gas. The observed ammonia structure mainly delineates the inner envelope around the central source. The velocity gradient is likely to originate in the angular momentum of the contracting core, although influence of the outflow from the neighbouring young star IRS4 is possibly visible on one side of the core. The tentative continuum detection and the indications of a warm background component near the rotation axis suggest that the core contains a deeply embedded outflow which may have been missed in previous single-dish CO surveys owing to beam dilution.
    Astronomy and Astrophysics 11/2013; 564. DOI:10.1051/0004-6361/201322069 · 4.38 Impact Factor