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Register a new userThe MESAS Project: Long wavelength follow-up observations of Sirius A
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Modeling the submillimeter to centimeter emission of stars is challenging due to a lack of sensitive observations at these long wavelengths. We launched an ongoing campaign to obtain new observations entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths (MESAS). Here we present ALMA, GBT, and VLA observations of Sirius A, the closest main-sequence A-type star, that span from 1.4 to 9.0 millimeters. These observations complement our previous millimeter data on Sirius A and are entirely consistent with the PHOENIX stellar atmosphere models constructed to explain them. We note that accurate models of long wavelength emission from stars are essential not only to understand fundamental stellar processes, but also to determine the presence of dusty debris in spatially unresolved observations of circumstellar disks.
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The spectrum of stars in the submillimeter to centimeter wavelength range remains poorly constrained due to a lack of data for most spectral types. An accurate characterization of stellar emission in this regime is needed to test stellar atmosphere models, and is also essential for revealing emission associated with unresolved circumstellar debris. We present ALMA observations of the three nearby, main-sequence, debris-poor, F-type stars $gamma$ Lep, $gamma$ Vir A, and $gamma$ Vir B at 0.87 and 1.29 millimeters. We use these data to constrain semi-empirical atmospheric models. We discuss the atmospheric structure of these stars, explore potential short term variability, and the potential impact on debris disk studies. These results are part of an ongoing campaign to obtain long wavelength observations of debris-poor stars, entitled Measuring the Emission of Stellar Atmospheres at Submillimeter/millimeter wavelengths (MESAS).
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We report on the results of multi-wavelength follow-up observations with Gemini, VLA, and ATCA, to search for a host galaxy and any persistent radio emission associated with FRB 180309. This FRB is among the most luminous FRB detections to date, with a luminosity of $> 8.7times 10^{32}$ erg Hz$^{-1}$ at the dispersion-based redshift upper limit of 0.32. We used the high-significance detection of FRB 180309 with the Parkes Telescope and a beam model of the Parkes Multibeam Receiver to improve the localization of the FRB to a region spanning approximately $sim2times2$. We aimed to seek bright galaxies within this region to determine the strongest candidates as the originator of this highly luminous FRB. We identified optical sources within the localization region above our r-band magnitude limit of 24.27, fourteen of which have photometric redshifts whose fitted mean is consistent with the redshift upper limit ($z < 0.32$) of our FRB. Two of these galaxies are coincident with marginally detected persistent radio sources of flux density 24.3$mu$Jy beam$^{-1}$ and 22.1$mu$Jy beam$^{-1}$ respectively. Our redshift-dependent limit on the luminosity of any associated persistent radio source is comparable to the luminosity limits for other localized FRBs. We analyze several properties of the candidate hosts we identified, including chance association probability, redshift, and presence of radio emission, however it remains possible that any of these galaxies could be the host of this FRB. Follow-up spectroscopy on these objects to explore their H$alpha$ emission and ionization contents, as well as to obtain more precisely measured redshifts, may be able to isolate a single host for this luminous FRB.
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