A Supersensitive Method for Spectroscopic Diagnostics of Electrostatic Waves in Magnetized Plasmas

For relatively strong magnetic fields, hydrogen atoms can have delocalized bound states of almost macroscopic dimensions. Therefore, such states are characterized by a Giant Electric Dipole Moment (GEDM), thus making them very sensitive to an external electric field. We considered the manifestations of the GEDM states in hydrogen spectral line profiles in the presence of a quasimonochromatic electrostatic wave of a frequency ω in a plasma. We demonstrated that in this situation, hydrogen spectral lines can exhibit quasi-satellites, which are the envelopes of Blochinzew-type satellites. We showed that the distinctive feature of such quasi-satellites is that their peak intensity is located at the same distance from the line center (in the frequency scale) for all hydrogen spectral lines, the distance being significantly greater than the wave frequency ω. At the absence of the GEDM (and for relatively strong electrostatic waves), the maxima of the satellite envelopes would be at different distances from the line center for different hydrogen lines. We demonstrated that this effect would constitute a supersensitive diagnostic method for measuring the amplitude of electrostatic waves in plasmas down to ~10 V/cm or even lower.

Photometric and spectroscopic analysis of LBV candidate J004341.84+411112.0 in M31

We study Luminous Blue Variable (LBV) candidate J004341.84+411112.0 in the Andromeda galaxy. We present optical spectra of the object obtained with the 6-m telescope of SAO RAS. The candidate shows typical LBV features in its spectra: broad and strong hydrogen lines and the HeI lines with P Cigni profiles. Its remarkable spectral resemblance to the well known LBV P Cygni suggests a common nature of the objects and supports LBV classification of J004341.84+411112.0. We estimate the temperature, reddening, radius and luminosity of the star using its spectral energy distribution. Obtained bolometric luminosity of the candidate (M bol = -10.40±0.12 mag) is quite similar to those of known LBV stars in the Andromeda galaxy. We analysed ten year light curve of the object in R filter. The candidate demonstrates photometric variations of the order of 0.4 mag, with an overall brightness increasing trend ΔR > 0.1 mag. Therewith, the corresponding colour variations of the object are fully consistent with LBV behavior when a star become cooler and brighter in the optical spectral range with a nearly constant bolometric luminosity. LBV-type variability of the object, similarity of its spectrum and estimated luminosity to those of known LBVs allows us to classify J004341.84+411112.0 as a LBV.

A high-resolution search for the Hα emission line of the accreting companion GQ Lup b with ESPRESSO

<p>In the current theories of planet formation, the amount of energy that a forming gas giant retains from its accretion flow is still unknown. This unconstrained parameter has a large impact on the post-formation evolution of the new planet, as it defines its initial temperature and luminosity. Models have been developed, ranging from “hot-start” models assuming that all the energy is retained internally, to “cold-start” ones assuming that everything is radiated away, and "warm-start" ones in between. Their coexistence introduces large degeneracies on the determination of age and mass in direct imaging observations, as these studies use the cold or hot-start models to infer these parameters from the observed luminosity of a planet. A promising way of solving this problem is the study of atomic emission lines originating from the hot gas shocked by the accretion flow. Recently, Aoyama et al. (2018, 2020) presented simulations of hydrogen lines emitted by the accretion shock onto the circumplanetary disk and the planetary surface. They showed that the line luminosity and width can be used to infer the protoplanet mass, thus giving an estimation that is independent from the evolution models. They applied it to the case of PDS70 b and c (Aoyama & Ikoma 2019, Hashimoto et al. 2020), but were ultimately limited by the spectral resolution of the MUSE observations they used (R ~ 2500). In this context, our team recently proposed and carried out a pilot program using the VLT/ESPRESSO fiber-fed spectrograph, equipped with very high resolution (R = 190 000), to characterize the Hα line of the young substellar companion GQ Lup b. We will present in this poster how these observations were conducted, the methods used to remove the contamination from the host star, and the results we obtained.</p>

Raman mapping of photodissociation regions

Broad Raman-scattered wings of hydrogen lines can be used to map neutral gas illuminated by high-mass stars in star forming regions. Raman scattering transforms far-ultraviolet starlight from the wings of the Lyβ line (1022Å to 1029Å) to red visual light in the wings of the Hα line (6400AA to 6700Å). Analysis of spatially resolved spectra of the Orion Bar and other regions in the Orion Nebula shows that this process occurs in the neutral photo-dissociation region between the ionization front and dissociation front. The inner Raman wings are optically thick and allow the neutral hydrogen density to be determined, implying n(H0) ≈ 105 cm−3 for the Orion Bar. Far-ultraviolet resonance lines of neutral oxygen imprint their absorption onto the stellar continuum as it passes through the ionization front, producing characteristic absorption lines at 6633Å and 6664Å with widths of order 2Å. This is a unique signature of Raman scattering, which allows it to be easily distinguished from other processes that might produce broad Hα wings, such as electron scattering or high-velocity outflows.

Analysis and modeling of the dynamics of the glow of calcium and hydrogen lines in solar and stellar flares

We present intensity curves of solar flares obtained in the Hα hydrogen line and CaII H, CaIR 8542Å lines using multichannel spectrographs of Ondřejov Observatory (Czech Republic) for the period 2000–2012. The general behavior of observed intensity curves is practically the same for all flares and is consistent with temporal variations of X-ray emission. However, our results differ significantly from those obtained by other authors for selected flare stars, for example, AD Leo; EV Lac; YZ CMi. We tried to explain the difference in the behavior of Ca II and Hα radiation flux by appearance of a shock wave during a flare and slow heating of the plasma.

Cloud-by-cloud, multiphase, Bayesian modelling: application to four weak, low-ionization absorbers

ABSTRACT We present a new method aimed at improving the efficiency of component by component ionization modelling of intervening quasar absorption-line systems. We carry out cloud-by-cloud, multiphase modelling making use of cloudy and Bayesian methods to extract physical properties from an ensemble of absorption profiles. Here, as a demonstration of method, we focus on four weak, low-ionization absorbers at low redshift, because they are multiphase but relatively simple to constrain. We place errors on the inferred metallicities and ionization parameters for individual clouds, and show that the values differ from component to component across the absorption profile. Our method requires user input on the number of phases and relies on an optimized transition for each phase, one observed with high resolution and signal-to-noise ratio. The measured Doppler parameter of the optimized transition provides a constraint on the Doppler parameter of H i, thus providing leverage in metallicity measurements even when hydrogen lines are saturated. We present several tests of our methodology, demonstrating that we can recover the input parameters from simulated profiles. We also consider how our model results are affected by which radiative transitions are covered by observations (for example, how many H i transitions) and by uncertainties in the b parameters of optimized transitions. We discuss the successes and limitations of the method, and consider its potential for large statistical studies. This improved methodology will help to establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the circumgalactic medium.

New luminous blue variable candidates in the NGC 247 galaxy

ABSTRACT We search for luminous blue variable (LBV) stars in galaxies outside the Local Group. Here we present a study of two bright Hα sources in the NGC 247 galaxy. Object j004703.27–204708.4 (MV = −9.08 ± 0.15 mag) shows the spectral lines typical for well-studied LBV stars: broad and bright emission lines of hydrogen and helium He i with P Cyg profiles, emission lines of iron Fe ii, silicon Si ii, nitrogen N ii and carbon C ii, forbidden iron [Fe ii] and nitrogen [N ii] lines. The variability of the object is ΔB = 0.74 ± 0.09 mag and ΔV = 0.88 ± 0.09 mag, which makes it a reliable LBV candidate. The star j004702.18–204739.93 (MV = −9.66 ± 0.23 mag) shows many emission lines of iron Fe ii, forbidden iron lines [Fe ii], bright hydrogen lines with broad wings, and also forbidden lines of oxygen [O i] and calcium [Ca ii] formed in the circumstellar matter. The study of the light curve of this star did not reveal significant variations in brightness (ΔV = 0.29 ± 0.09 mag). We obtained estimates of interstellar absorption, the photosphere temperature, as well as bolometric magnitudes $M_\text{bol}=-10.5^{+0.5}_{-0.4}$ and $M_\text{bol}=-10.8^{+0.5}_{-0.6}$, which correspond to bolometric luminosities $\log (L_\text{bol}/{\rm L}_{\odot })=6.11^{+0.20}_{-0.16}$ and $6.24^{+0.20}_{-0.25}$ for j004703.27–204708.4 and j004702.18–204739.93, respectively. Thus, the object j004703.27–204708.4 remains a reliable LBV candidate, while the object j004702.18–204739.93 can be classified as a B[e]-supergiant.

Luminous blue variable candidates in M31

ABSTRACT We study five luminous blue variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-m telescope at the Apache Point Observatory and on the 6-m telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, He i, Fe ii, and [Fe ii] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known LBV stars in the Andromeda galaxy. One candidate, J004341.84+411112.0, demonstrates photometric variability (about 0.27 mag in the V band), which allows us to classify it as an LBV. The star J004415.04+420156.2 shows characteristics typical of B[e] supergiants. The star J004411.36+413257.2 is classified as a Fe ii star. We confirm that the stars J004621.08+421308.2 and J004507.65+413740.8 are warm hypergiants. We obtain for the first time the NIR spectrum of the Galactic LBV candidate MN112. We use both optical and NIR spectra of MN112 for comparison with similar stars in M31 and notice identical spectra and the same temperature in J004341.84+411112.0. This allows us to confirm that MN112 is an LBV, which should show its brightness variability in longer time span observations.

Modelling spectra of MN112

ABSTRACT MN112 is a Galactic luminous blue variable (LBV) candidate with a circumstellar nebula. P Cygni was the first LBV discovered, and was recorded during major eruptions in the 17th century. The stars have similar spectra with strong emission hydrogen lines, He i, N ii, Si ii, and Fe iii lines. We present the results of spectroscopic analysis and modelling of MN112 spectra. We obtained the main stellar parameters and chemical abundances of MN112 and compared them with those of P Cygni. Atmosphere models were calculated using the non-local thermodynamic equilibrium radiative transfer code cmfgen. We have used spectra of MN112 obtained with the 3.5-m telescope at the Observatory of Calar Alto and 3.5-m ARC telescope at the Apache Point Observatory. P Cygni spectra were taken with the 6-m BTA telescope. We have found the best fit of the observed spectrum with the model at temperature $T_{\text{eff}}= 15\, 200$ K, clumping-corrected mass-loss rate $\dot{M}f^{-0.5}=5.74 \times 10^{-5}\, \mathrm{M}_{\odot }\text{yr}^{-1}$, filling factor f = 0.1, luminosity $L=5.77 \times 10^5\, \mathrm{L}_{\odot }$ for MN112. The ratio of helium to hydrogen He/H is 0.27 (by the number of atoms) with nitrogen overabundance (XN/X⊙ = 6.8) and an underabundance of carbon (XC/X⊙ < 0.1).