Herschel-HIFI News

Submitted by Sylvie Beaulieu, Herschel-HIFI Instrument Support Scientist
(Cassiopeia – Winter 2014)
Herschel_spacecraft_artist410

Feature story – Detection of an Anomalous Hot Gas Component in a Low Mass Star-Forming Region

By Andy Pon (2014 Plaskett medal recipient; Leeds University)

Using HIFI on Herschel, the CO (5-4) and CO (6-5) transitions were observed towards the centre of Perseus B1-E5, a starless condensation in the Perseus molecular cloud, which is a nearby low mass star-forming region. HIFI obtained strong detections of two separate velocity components in both transitions.

Photodissociation region (PDR) models from the Kaufman et al. (1996), KOSMA-tau, and Meudon codes were compared to a spectral energy diagram composed of the HIFI data and archival data of lower J CO lines. The PDR models were able to account for the emission in the CO (1-0), (3-2) and (5-4) lines, but every model that fit these lower lines significantly underpredicted the integrated intensity of the (6-5) line. This inability
of the PDR models to consistently account for the CO (6-5) emission implies that there is a warm gas component within B1-E5 that is not included in standard PDR models.

Given the lack of any protostars or protostellar outflows in the vicinity of B1-E5, the most plausible source of this warm gas is the dissipation of turbulence in low velocity shocks. The observed emission is consistent with the turbulent energy dissipating on a timescale a factor of three larger than the turbulent crossing time. Only 0.15% of the gas within B1-E5 would need to be shock heated by 3 km/s shocks to explain the observed CO (6-5) integrated intensities.

This work is described in more detail in Pon et al. (2014, MNRAS, 445, 1508).

The lines show the best fitting KOSMA-tau models to the observed integrated intensity  ratios for the two detected components. Note that the models fail to reproduce the large  CO (6-5) intensities.

The lines show the best fitting KOSMA-tau models to the observed integrated intensity
ratios for the two detected components. Note that the models fail to reproduce the large
CO (6-5) intensities.

Herschel Interactive Processing Environment (HIPE)

HIPE 12.1 is the current released version. Please visit ‘What’s New in HIPE‘ for the latest changes in this release. Additional information can be found in the ‘HIFI Instrument and Calibration‘ webpage.

Note that HIPE 13 is currenty being tested and will be available in the Spring.

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