On the association of G343.1-2.3 and PSR 1706-44

The association of G343.1-2.3 and PSR 1706-44 has been controversial from its first proposal. In this paper we address the difficulties, and argue that the association is still likely. New evidence comes from images of G343.1-2.3 obtained using the Australia Telescope Compact Array (ATCA), and the pulsar obtained using the CHANDRA X-ray observatory. Mosaicing was required to cover the full extent of G343.1-2.3, and we present the polarisation images from this experiment. Also an X-ray pulsar wind nebula has been found in the archived CHANDRA observations, with the correct morphology to support the association. The ATCA observations confirm the much larger extent of the SNR, which now encompasses the pulsar. The X-ray morphology points back toward the centre of the SNR, indicating the direction of the proper motion, and that the PSR and SNR are associated.Comment: 11 pages, 5 figures, submitted to MNRA

Line Ratios Reveal N2H+ Emission Originates Above the Midplane in TW Hydrae

Line ratios for different transitions of the same molecule have long been used as a probe of gas temperature. Here we use ALMA observations of the N2H+ J~=~1-0 and J~=~4-3 lines in the protoplanetary disk around TW Hya to derive the temperature at which these lines emit. We find an averaged temperature of 39~K with a one sigma uncertainty of 2~K for the radial range 0.8-2'', significantly warmer than the expected midplane temperature beyond 0.5'' in this disk. We conclude that the N2H+ emission in TW Hya is not emitting from near the midplane, but rather from higher in the disk, in a region likely bounded by processes such as photodissociation or chemical reprocessing of CO and N2 rather than freeze out.Comment: Accepted for publication in ApJ Letters, 5 pages, 1 figur

A recent accretion burst in the low-mass protostar IRAS 15398-3359: ALMA imaging of its related chemistry

Low-mass protostars have been suggested to show highly variable accretion rates through-out their evolution. Such changes in accretion, and related heating of their ambient envelopes, may trigger significant chemical variations on different spatial scales and from source-to-source. We present images of emission from C17O, H13CO+, CH3OH, C34S and C2H toward the low-mass protostar IRAS 15398-3359 on 0.5" (75 AU diameter) scales with the Atacama Large Millimeter/submillimeter Array (ALMA) at 340 GHz. The resolved images show that the emission from H13CO+ is only present in a ring-like structure with a radius of about 1-1.5" (150-200 AU) whereas the CO and other high dipole moment molecules are centrally condensed toward the location of the central protostar. We propose that HCO+ is destroyed by water vapor present on small scales. The origin of this water vapor is likely an accretion burst during the last 100-1000 years increasing the luminosity of IRAS 15398-3359 by a factor of 100 above its current luminosity. Such a burst in luminosity can also explain the centrally condensed CH3OH and extended warm carbon-chain chemistry observed in this source and furthermore be reflected in the relative faintness of its compact continuum emission compared to other protostars.Comment: Accepted for publication in ApJ Letters; 14 pages, 5 figure