Detecting shock waves in non-fundamental mode RR Lyrae using large sample of spectra in SDSS and LAMOST

Steps toward the nature inside RR Lyrae variables can not only improve our understanding of variable stars but also innovate the precision when we use them as tracers to map the structure of the universe. In this work, we develop a hand-crafted one-dimensional pattern recognition pipeline to fetch out the "first apparitions", the most prominent observational characteristic of shock. We report the first detection of hydrogen emission lines in the first-overtone and multi-mode RR Lyrae variables. We find that there is an anti-correlation between the intensity and the radial velocity of the emission signal, which is possibly caused by opacity changing in the helium ionization zone. Moreover, we find one RRd star with hydrogen emission that possibly shows Blazhko-type modulations. According to our discoveries, with an enormous volume of upcoming data releases of variable stars and spectra, it may become possible to build up the bridge between shock waves and big problems like the Blazhko effect in non-fundamental mode RR Lyrae stars.

A new take on the low-mass brown dwarf companions on wide orbits in Upper-Scorpius

Context. The Upper-Scorpius association (5–11 Myr) contains a unique population of low-mass (M ≤ 30MJup) brown dwarfs either free-floating, forming wide pairs, or on wide orbits around solar-type and massive stars. The detailed relative characterization of their physical properties (mass, radius, temperature, composition, and ongoing accretion) offers the opportunity to potentially explore their origin and mechanisms of formation. Aims. In this study, we aim to characterize the chemical and physical properties of three young, late-M brown dwarfs claimed to be companions of the Upper-Scorpius stars USco 161031.9-16191305, HIP 77900, and HIP 78530 using medium-resolution spectroscopy at UV (0.30−0.56μm; Rλ ~ 3300), optical (0.55−1.02μm; Rλ ~ 5400), and NIR (1.02−2.48μm; Rλ ~ 4300) wavelengths. The spectra of six free-floating analogs from the same association are analyzed for comparison and to explore the potential physical differences between these substellar objects found in different configurations. We also aim to examine and analyze hydrogen emission lines at UV and optical wavelengths to investigate the presence of ongoing accretion processes. Methods. The X-shooter spectrograph at VLT was used to obtain the spectra of the nine young brown dwarfs over the 0.3−2.5μm range simultaneously. Performing a forward modeling of the observed spectra with the ForMoSA code, we infer the Teff, log (g), and radius of our objects. The code compares here the BT-SETTL15 models to the observed spectra using the Nested Sampling Bayesian inference method. Mass is determined using evolutionary models, and a new analysis of the physical association is presented based on Gaia-DR2 astrometry. Results. The Teff and log (g) determined for our companions are compatible with those found for free-floating analogs of the Upper-Scorpius association and with evolutionary model predictions at the age of the association. However the final accuracy on the Teff estimates is strongly limited by nonreproducibility of the BT-SETTL15 models in the range of Teff corresponding to the M8–M9 spectral types. We identified Hα, Hβ, Hγ, and Ca II H and K emission lines in the spectrum of several objects. We attribute these lines to chromospheric activity except for the free-floating object USco 1608-2315 for which they are indicative of active accretion (M˙ ≤ 10−10.76 M⊙ yr−1). We confirm the four-fold over-luminosity of USco 161031.9-16191305 B down to 0.3 μm, which could be explained in part by the activity of this object and if the companion is an unresolved multiple system.

Spectral index in the radio continuum 140 MHz – 1.4 GHz emission for compact star-forming galaxies

The sample of compact star-forming galaxies (CSFGs) has been identified with sources in the catalogues of radio sources. It includes only galaxies with active star formation without objects with spectral signs of active galactic nuclei. For CSFGs with known flux densities in radiocontinuum at frequencies of 1.4 GHz from the FIRST or the NVSS and in the range of 120–168 MHz from the LOFAR, as well as in hydrogen emission lines from the SDSS, the spectral index and the spectral index of non-thermal emission component for these frequencies have been estimated. Note that obtaining the spectral index of nonthermal emission component is a much more difficult task than determining the spectral index of total emission. It is shown that the approximation by the model dependence using the least squares method can lead to unreliable estimates of the fraction of thermal (free-free) emission. Therefore, the flux densities of the thermal component are derived from the extinction- and aperture corrected fluxes of the Hα emission line. This method of estimation without using a fitting is more reliable. It is shown that the fact that derived spectra in radio range are quite flat is due, in particular, to the influence of selection effects caused by limited sensitivity of radio telescopes. For the same reason, only galaxies with a small fraction of thermal emission were included in the sample. Therefore, the spectral index is not much different from the spectral index of non-thermal emission.

SBS 0802+529: A New Variable Star from the Second Byurakan Survey

A new emission line star was discovered on the plates of the Second Byurakan Survey (SBS). the follow up spectroscopy demonstrated that the object had a spectrum dominated by a late-type giant star with superposed hydrogen emission lines. the object resembles a pulsating Mira, but the amplitude of variability and a rapid UV variability are quite unusual for a single star, and we tentatively classify the object as a symbiotic star.

K- and L-band spectroscopy of Be stars

We describe the behaviour of IR hydrogen emission lines of a sample of Be stars and discuss the physical properties of the circumstellar envelopes of Be stars classified in Groups I and II (Mennickent et al. 2009). We find that while Humphreys and Pfund lines of Group I stars form in an optically thick envelope/disk, Group II stars show Pfund lines that form in an optically thick medium and Humphreys lines originating in optically thinner regions. The transition between Groups I and II could be understood in terms of the evolution of the circumstellar disk of the star and might bring clues on the mechanism originating the Be phenomenon.