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Abstract We investigate the relationship between dust attenuation and stellar mass ( M * ) in star-forming galaxies over cosmic time. For this analysis, we compare measurements from the MOSFIRE Deep Evolution Field survey at z ∼ 2.3 and the Sloan Digital Sky Survey (SDSS) at z ∼ 0, augmenting the latter optical data set with both UV Galaxy Evolution Explorer (GALEX) and mid-infrared Wide-field Infrared Survey Explorer (WISE) photometry from the GALEX-SDSS-WISE Catalog. We quantify dust attenuation using both spectroscopic measurements of H α and H β emission lines, and photometric measurements of the rest-UV stellar continuum. The H α /H β ratio is used to determine the magnitude of attenuation at the wavelength of H α , A H α . Rest-UV colors and spectral energy distribution fitting are used to estimate A 1600 , the magnitude of attenuation at a rest wavelength of 1600 Å. As in previous work, we find a lack of significant evolution in the relation between dust attenuation and M * over the redshift range z ∼ 0 to z ∼ 2.3. Folding in the latest estimates of the evolution of M dust , ( M dust / M gas ), and gas surface density at fixed M * , we find that the expected M dust and dust mass surface density are both significantly higher at z ∼ 2.3 than at z ∼ 0. These differences appear at odds with the lack of evolution in dust attenuation. To explain the striking constancy in attenuation versus M * , it is essential to determine the relationship between metallicity and ( M dust / M gas ), the dust mass absorption coefficient and dust geometry, and the evolution of these relations and quantities from z ∼ 0 to z ∼ 2.3.
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Outbursts and stellar properties of the classical Be star HD 6226
ABSTRACT The bright and understudied classical Be star HD 6226 has exhibited multiple outbursts in the last several years during which the star grew a viscous decretion disc. We analyse 659 optical spectra of the system collected from 2017 to 2020, along with a ultraviolet spectrum from the Hubble Space Telescope and high cadence photometry from both Transiting Exoplanet Survey Satellite (TESS) and the Kilodegree Extremely Little Telescope (KELT) survey. We find that the star has a spectral type of B2.5IIIe, with a rotation rate of 74 per cent of critical. The star is nearly pole-on with an inclination of 13$${_{.}^{\circ}}$$4. We confirm the spectroscopic pulsational properties previously reported, and report on three photometric oscillations from KELT photometry. The outbursting behaviour is studied with equivalent width measurements of H α and H β, and the variations in both of these can be quantitatively explained with two frequencies through a Fourier analysis. One of the frequencies for the emission outbursts is equal to the difference between two photometric oscillations, linking these pulsation modes to the mass ejection mechanism for some outbursts. During the TESS observation time period of 2019 October 7 to 2019 November 2, the star was building a disc. With a large data set of H α and H β spectroscopy, we are able to determine the time-scales of dissipation in both of these lines, similar to past work on Be stars that has been done with optical photometry. HD 6226 is an ideal target with which to study the Be disc-evolution given its apparent periodic nature, allowing for targeted observations with other facilities in the future.
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- Award ID(s):
- 1908026
- PAR ID:
- 10350096
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 508
- Issue:
- 2
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 2002 to 2018
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1093/mnras/stab2759
