Anita M. S. Richards

e-MERLIN resolves Betelgeuse at λ 5 cm: hotspots at 5 R⋆

Convection, pulsation and magnetic fields have all been suggested as mechanisms for the transport of mass and energy from the optical photosphere of red supergiants, out to the region where the stellar wind is launched. We imaged the red supergiant Betelgeuse at 0.06-0.18 arcsec resolution, using e-MERLIN at 5.5--6.0 GHz, with a sensitivity of ~0.01 mJy/beam. Most of the radio emission comes from within an ellipse (0.235x0.218) arcsec^2 (~5x the optical radius), with a flux density of 1.62 mJy, giving an average brightness temperature ~1250 K. This radio photosphere contains two hotspots of 0.53 and 0.79 mJy/beam, separated by 90 milli-arcsec, with brightness temperatures 5400+/-600 K and 3800+/-500 K. Similar hotspots, at more than double the distance from the photosphere of those seen in any other regime, were detected by the less-sensitive `old MERLIN in 1992, 1995 and 1996 and many exceed the photospheric temperature of 3600 K. Such brightness temperatures are high enough to emanate from pockets of chromospheric plasma. Other possibilities include local shock heating, the convective dredge-up of hot material or exceptionally cool, low density regions, transparent down to the hottest layer at ~40 milliarcsec radius. We also detect an arc 0.2--0.3 arcsec to the SW, brightness temperature ~150 K, in a similar direction to extensions seen on both smaller and larger scales in the infra-red and in CO at mm wavelengths. These preliminary results will be followed by further e-MERLIN, VLA and ALMA observations to help resolve the problem of mass elevation from 1 to 10 R* in red supergiants.

The inhomogeneous submillimeter atmosphere of Betelgeuse

The mechanisms responsible for heating the extended atmospheres of early-M spectral-type supergiants are poorly understood. So too is the subsequent role these mechanisms play in driving the large mass-loss rates of these stars. Here we present ALMA long (i.e., ~16u2009km) baseline 338u2009GHz (0.89u2009mm) continuum observations of the free-free emission in the extended atmosphere of the M2 spectral-type supergiant Betelgeuse. The spatial resolution of 14u2009mas exquisitely resolves the atmosphere, revealing it to have a mean temperature of 2760u2009K at ~1.3u2009 R ⋆ , which is below both the photospheric effective temperature ( T eff = 3690 K) and the temperatures at ~2 R ⋆ . This is unambiguous proof for the existence of an inversion of the mean temperature in the atmosphere of a red supergiant. The emission is clearly not spherically symmetric with two notable deviations from a uniform disk detected in both the images and visibilities. The most prominent asymmetry is located in the north-east quadrant of the disk and is spatially resolved showing it to be highly elongated with an axis-ratio of 2.4 and occupying ~5% of the disk projected area. Its temperature is approximately 1000u2009K above the measured mean temperature at 1.3u2009 R ⋆ . The other main asymmetry is located on the disk limb almost due east of the disk center and occupies ~3% of the disk projected area. Both emission asymmetries are clear evidence for localized heating taking place in the atmosphere of Betelgeuse. We suggest that the detected localized heating is related to magnetic activity generated by large-scale photospheric convection.

Vibrationally excited water emission at 658 GHz from evolved stars

Several rotational transitions of water have been identified toward evolved stars in the ground vibrational state as well as in the first excited state of the bending mode. In the latter vibrational state of water, the 658 GHz J = 1_1,0-1_0,1 rotational transition is often strong and seems to be widespread in late-type stars. Our main goals are to better characterize the nature of the 658 GHz emission, compare the velocity extent of the 658 GHz emission with SiO maser emission to help locate the water layers and, more generally, investigate the physical conditions prevailing in the excited water layers of evolved stars. Another goal is to identify new 658 GHz emission sources and contribute in showing that this emission is widespread in evolved stars. Eleven evolved stars were extracted from our mini-catalog of existing and potential 658 GHz sources for observations with the APEX telescope equipped with the SEPIA receiver. The 13CO J=6-5 line was placed in the same receiver sideband for simultaneous observation with the 658 GHz line of water. We have compared the 658 GHz line properties with our H2O radiative transfer models in stars and we have compared the velocity ranges of the 658 GHz and SiO J=2-1, v=1 maser lines. All stars show 658 GHz emission with a peak flux density in the range 50-70 Jy to 2000-3000 Jy. We have shown that the 658 GHz line is masing and we found that the 658 GHz velocity extent tends to be correlated with that of the SiO maser suggesting that both emission lines are excited in circumstellar layers close to the central star. Broad and stable line profiles are observed at 658 GHz. This could indicate maser saturation although we have tentatively provided first information on time variability at 658 GHz.

OH MASERS TOWARDS THE W49A STAR-FORMING REGION WITH MERLIN AND e-MERLN OBSERVATIONS

We present preliminary results from OH ground state phase referenced observations carried out with the Multi Element Radio Linked Interferometer Network (MERLIN) and e-MERLIN towards the massive star forming region W49A. There are three active SFRs within this complex: W49 North (W49 N), W49 South (W49 S) and W49 South West (W49 SW). The rst epoch of observations was obtained in 2005 with MERLIN while the second epoch was obtained in 2013 with the e-MERLIN upgraded system. In this paper, we present 1665 and 1720 MHz maser emission towards W49 S and W49 SW. Overall, both epochs show good agreement with the previous observations of Argon et al. (2000) carried out with the Very Large Array (VLA). The better sensitivity and wider velocity coverage of the MERLIN/e-MERLIN observations allowed us to discover a new 1720 MHz OH maser site in W49 S.

MERLIN and eMERLIN OH maser observations toward the star forming region complex W49 A

Kitiyanee Asanok1, Sandra Etoka∗2, Malcolm Gray3, Anita Richards3; Busaba-Hutawarakorn Kramer4,5, Nipon Gasiprong6 1 Khon Kaen University, TH; 2Hamburger Sternwarte, DE; 3 Jodrell Bank Centre for Astrophysics, UK; 4 Max-Planck-Institut für Radioastronomie, DE; 5 National Astronomical Research Institute of Thailand, TH; 6 Ubon Ratchathani University, TH E-mail: kitiyanee@kku.ac.th / sandra.etoka@googlemail.com

Maser observations - from the kinematics to the physics of evolved star winds.

M13 9PL, UK. cSwinburne University of Technology, Victoria, Australia dToruń Centre for Astronomy, Nicolaus Copernicus Universi ty, Poland e University of Kentucky, Department of Physics and Astronom y, USA f ESO, D-85748 Garching-bei-München, Germany gMPIfR, 53121 Bonn, Germany hLeiden University & JIVE, PO Box 2, NL-7990 AA Dwingeloo, NL iDepartment of Physics and Astronomy, UCL, London WC1E 6BT, U K