Near-infrared Studies of Nova V1674 Herculis: A Shocking Record Breaker

We present near-infrared spectroscopy of Nova Herculis 2021 (V1674 Her), obtained over the first 70 days of its evolution. This fastest nova on record displays a rich emission line spectrum, including strong coronal line emission with complex structures. The hydrogen line fluxes, combined with a distance of 4.7 − 1.0 + 1.3 kpc, give an upper limit to the hydrogen ejected mass of M ej = 1.4 − 1.2 + 0.8 × 10 − 3 M ⊙. The coronal lines appeared at day 11.5, the earliest onset yet observed for any classical nova, before there was an obvious source of ionizing radiation. We argue that the gas cannot be photoionized, at least in the earliest phase, and must be shocked. Its temperature is estimated to be 105.57±0.05 K on day 11.5. Tentative analysis indicates a solar abundance of aluminum and an underabundance of calcium, relative to silicon, with respect to solar values in the ejecta. Further, we show that the vexing problem of whether collisional ionization or photoionization is responsible for coronal emission in classical novae can be resolved by correlating the temporal sequence in which the X-ray supersoft phase and the near-infrared coronal line emission appear.

The importance of the diffuse ionized gas for interpreting galaxy spectra

Diffuse ionized gas (DIG) in galaxies can be found in early-type galaxies, in bulges of late-type galaxies, in the interarm regions of galaxy disks, and outside the plane of such disks. The emission-line spectrum of the DIG can be confused with that of a weakly active galactic nucleus. It can also bias the inference of chemical abundances and star formation rates in star forming galaxies. We discuss how one can detect and feasibly correct for the DIG contribution in galaxy spectra.

The enigmatic binary system HD 5980

The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich Wolf–Rayet (WR) star. Since the eruption, the wind mass-loss rate has been declining while wind speeds have been steadily increasing. Observations obtained in 2014 when Star A (the LBV) eclipses Star B indicate that the fitted mass-loss rate and luminosity have reached the lowest values ever determined for such spectra: $\dot{M}$ = 4.5 × 10−5$\mathrm{M}_\odot \, \hbox{yr}^{-1}$, L = 1.7 × 106 L⊙. In addition, the radius of the LBV’s continuum-emitting region is similar to that derived from the eclipse light curves of the late 1970s. Hence, it appears to have attained a similar ‘low’ state to that of the late 1970s. While a good fit to the emission spectrum is obtained using a cmfgen model, there are discrepancies in the UV. In particular, the extent of the observed absorption profiles is ∼1000 km s−1 greater than predicted by the emission-line intensities. Further, HST UV observations obtained in 2016, when Star A is eclipsed by Star B, show unusual P Cygni profiles that are not easily explained. Surprisingly the 2016 emission-line spectrum is similar to that at the opposite eclipse obtained in 2014. The complex UV profiles are likely to arise as a consequence of the dynamics of the wind–wind collision and radiative braking, both of which will cause significant departures from spherical symmetry, and have a strong orbital phase dependence. However, other scenarios, such as intrinsically aspherical winds, cannot be ruled out.

Pengaruh Medan Magnetik Eksternal pada Tabung Gas Hidrogen terhadap Spektrum Emisi pada Efek Zeeman

This study aims to know what will happen when the emission line spectrum emitted by gas tube of the hydrogen atom electron at certain wavelength passed in an external magnetic field. This study was analyzed by non quantitaive comparing between without field and with an external magnetic field. Based on the results of research done obtained a result that the emission spectrum of hydrogen gas passed in an external magnetic field changed the intensity of spectrum. The larger intensity of the magnetic field radiated, that shows where the larger magnetic field used the larger distance split of spectral line .

The accretion process in the magnetic Herbig Ae star HD 104237

After successfully retrieving the known rotation period P = 42.076 d in the Herbig Ae star HD 101412 using spectroscopic signatures of accretion tracers (Schöller et al.2016), we have studied magnetospheric accretion in the Herbig Ae SB2 system HD 104237 using spectroscopic parameters of the He i 10830, Paγ, and He i 5876 lines, formed in the accretion region. Employing 21 spectra obtained with ISAAC and X-shooter, we found that the temporal behavior of these parameters can be explained by a variable amount of matter being accreted in the region between the star and the observer. Using a periodogram analysis, we examined the possible origin of the accretion flow in HD 104237 and considered the following four scenarios: matter flows from the circumbinary envelope, mass exchange between the system’s components, magnetospheric accretion (MA) from the disk onto the star, and fast high-latitude accretion from a disk wind onto a weakly magnetized star. Based on a correlation analysis, we were able to show that the primary component is responsible for the observed emission line spectrum of the system. Since we do not find any correlation of the spectroscopic parameters with the phase of the orbital period (P ≍ 20 d), we can reject the first two scenarios. We found a variation period of about 5 d, which likely represents the stellar rotation period of the primary and favors the MA scenario.

Line-dependent veiling in very active classical T Tauri stars

Context. The T Tauri stars with active accretion disks show veiled photospheric spectra. This is supposedly due to non-photospheric continuum radiated by hot spots beneath the accretion shocks at stellar surface and/or chromospheric emission lines radiated by the post-shocked gas. The amount of veiling is often considered as a measure of the mass-accretion rate. Aim. We analysed high-resolution photospheric spectra of accreting T Tauri stars LkHα 321, V1331 Cyg, and AS 353A with the aim of clarifying the nature of the line-dependent veiling. Each of these objects shows a strong emission line spectrum and powerful wind features indicating high rates of accretion and mass loss. Methods. Equivalent widths of hundreds of weak photospheric lines were measured in the observed spectra of high quality and compared with those in synthetic spectra of appropriate models of stellar atmospheres. Results. The photospheric spectra of the three T Tauri stars are highly veiled. We found that the veiling is strongly line-dependent: larger in stronger photospheric lines and weak or absent in the weakest ones. No dependence of veiling on excitation potential within 0 to 5 eV was found. Different physical processes responsible for these unusual veiling effects are discussed in the framework of the magnetospheric accretion model. Conclusions. The observed veiling has two origins: (1) an abnormal structure of stellar atmosphere heated up by the accreting matter, and (2) a non-photospheric continuum radiated by a hot spot with temperature lower than 10 000 K. The true level of the veiling continuum can be derived by measuring the weakest photospheric lines with equivalent widths down to ≈10 mÅ. A limited spectral resolution and/or low signal-to-noise ratio results in overestimation of the veiling continuum. In the three very active stars, the veiling continuum is a minor contributor to the observed veiling, while the major contribution comes from the line-dependent veiling.

The very fast evolution of Sakurai's object

V4334 Sgr (a.k.a. Sakurai's object) is the central star of an old planetary nebula that underwent a very late thermal pulse a few years before its discovery in 1996. We have been monitoring the evolution of the optical emission line spectrum since 2001. The goal is to improve the evolutionary models by constraining them with the temporal evolution of the central star temperature. In addition the high resolution spectral observations obtained by X-shooter and ALMA show the temporal evolution of the different morphological components.

Confirmation of the Luminous Blue Variable Status of MWC 930

We present spectroscopic and photometric observations of the emission-line star MWC 930 (V446 Sct) during its long-term optical brightening in 2006–2013. Based on our earlier data we suggested that the object has features found in Luminous Blue Variables (LBV), such as a high luminosity (~3 105 L⊙), a low wind terminal velocity (~140 km s−1), and a tendency to show strong brightness variations (~1 mag over 20 years). For the last~7 years it has been exhibiting a continuous optical and near-IR brightening along with a change of the emission-line spectrum appearance and cooling of the star’s photosphere. We present the object’sV-band light curve, analyze the spectral variations, and compare the observed properties with those of other recognized Galactic LBVs, such as AG Car and HR Car. Overall we conclude the MWC 930 is a bona fide Galactic LBV that is currently in the middle of an S Dor cycle.