We determine the velocity distribution and space density of a volume complete sample of A and F stars, using parallaxes and proper motions from the Hipparcos satellite. We use these data to solve for the gravitational potential vertically in the local Galactic disc, by comparing the Hipparcos measured space density with predictions from various disc models. We derive an estimate of the local dynamical mass density of 0.102 +/- 0.010 solar masses per cubic parsec which may be compared to an estimate of 0.095 solar masses per cubic parsec in visible disc matter. Our estimate is found to be in reasonable agreement with other estimates by Creze et al. and Pham, also based on Hipparcos data. We conclude that there is no compelling evidence for significant amounts of dark matter in the disc.Comment: 9 pages, 7 figures, accepted by MNRA

We measure the volume luminosity density and surface luminosity density generated by the Galactic disc, using accurate data on the local luminosity function and the vertical structure of the disc. From the well-measured volume mass density and surface mass density, we derive local volume and surface mass-to-light ratios (M/L) for the Galactic disc, in the bands B, V and I. We obtain M/L for the local column of stellar matter of (M/L) B = 1.4 ± 0.2, (M/L) V = 1.5 ± 0.2 and (M/L) I = 1.2 ± 0.2. The dominant contributors to the surface luminosity in these bands are main-sequence turnoff stars and giants. Our results on the colours and M/L for the 'solar cylinder' well agree with population synthesis predictions using initial mass functions typical of the solar neighbourhood. Finally, we infer the global luminosity of the Milky Way, which appears to be underluminous by about 1σ with respect to the main locus of the Tully-Fisher relation, as observed for external galaxies.

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Fast Radio Bursts (FRBs) are brief radio emissions from distant astronomical sources. Some are known to repeat, but most are single bursts. Non-repeating FRB observations have had insufficient positional accuracy to localize them to an individual host galaxy. We report the interferometric localization of the single pulse FRB 180924 to a position 4 kpc from the center of a luminous galaxy at redshift 0.3214. The burst has not been observed to repeat. The properties of the burst and its host are markedly different from the only other accurately localized FRB source. The integrated electron column density along the line of sight closely matches models of the intergalactic medium, indicating that some FRBs are clean probes of the baryonic component of the cosmic web.Cosmological observations have shown that baryons comprise 4% of the energy density of the Universe, of which only about 10% is in cold gas and stars (1), with the remainder residing in a diffuse plasma surrounding and in between galaxies and galaxy clusters. The location and density of this material has been challenging to characterize, and up to 50% of it remains unaccounted (2).Fast radio bursts (FRBs; ref.(3)) are bright bursts of radio waves with millisecond duration. They can potentially be used to detect, study, and map this medium, as bursts of emission are dispersed and scattered by their 1 arXiv:1906.11476v1 [astro-ph.HE] 27 Jun 2019 dual-polarization beams on the sky using digital beamforming, producing a total field-of-view of ∼ 30 deg 2 . For burst detection, the beamformers produces channelized autocorrelation spectra for both linear polarizations of all beams, with an integration time of 864 µs and channel bandwidth of 1 MHz in these observations. We used 336 channels centered at 1320 MHz. A real-time detection pipeline incoherently adds the spectra from all available antennas (24 antennas in these observations) and polarization channels, then searches (16) the result for dispersed pulses (17).Burst localization is completed with a second data product that utilizes both the amplitude and phase information of the burst radiation. The beamformers store samples of the complex electric field for all beams and both polarizations in a ring buffer of 3.1 s duration, with the oldest data being continuously overwritten by new data. The data are saved for offline interferometric analysis only when the pipeline identifies a candidate. For the searches reported here the triggering required pulses with widths less than 9 ms and S/N > 10.Previous searches with ASKAP used antennas pointed in different directions to maximize sky coverage (10,16). In contrast, our observations used antennas all pointed in the same direction, enabling the array to act as an interferometer capable of sub-arcsecond localization with a 30 deg 2 field of view. We targeted high Galactic latitude fields (Galactic latitude |b| ∼ 50 • ), that had been observed previously (10, 16), and Southern circumpolar fields. The high-latitude fields were observed regularly through 2017 and earl...

We derive an empirical effective temperature and bolometric luminosity calibration for G and K dwarfs, by applying our own implementation of the Infrared Flux Method to multiband photometry. Our study is based on 104 stars for which we have excellent BV(RI ) C JHK S photometry, excellent parallaxes and good metallicities.Colours computed from the most recent synthetic libraries (ATLAS9 and MARCS) are found to be in good agreement with the empirical colours in the optical bands, but some discrepancies still remain in the infrared. Synthetic and empirical bolometric corrections also show fair agreement.A careful comparison to temperatures, luminosities and angular diameters obtained with other methods in the literature shows that systematic effects still exist in the calibrations at the level of a few per cent. Our Infrared Flux Method temperature scale is 100-K hotter than recent analogous determinations in the literature, but is in agreement with spectroscopically calibrated temperature scales and fits well the colours of the Sun. Our angular diameters are typically 3 per cent smaller when compared to other (indirect) determinations of angular diameter for such stars, but are consistent with the limb-darkening corrected predictions of the latest 3D model atmospheres and also with the results of asteroseismology.Very tight empirical relations are derived for bolometric luminosity, effective temperature and angular diameter from photometric indices.We find that much of the discrepancy with other temperature scales and the uncertainties in the infrared synthetic colours arise from the uncertainties in the use of Vega as the flux calibrator. Angular diameter measurements for a well-chosen set of G and K dwarfs would go a long way to addressing this problem.