Hα Emission Profiles Research Articles

Time-varying double-peaked emission lines following the sudden ignition of the dormant galactic nucleus AT2017bcc

ABSTRACT We present a pan-chromatic study of AT2017bcc, a nuclear transient that was discovered in 2017 within the skymap of a reported burst-like gravitational-wave candidate, G274296. It was initially classified as a superluminous supernova, and then reclassified as a candidate tidal disruption event. Its optical light curve has since shown ongoing variability with a structure function consistent with that of an active galactic nucleus, however, earlier data show no variability for at least 10 yr prior to the outburst in 2017. The spectrum shows complex profiles in the broad Balmer lines: a central component with a broad-blue wing, and a boxy component with time-variable blue and red shoulders. The H α emission profile is well modelled using a circular accretion disc component, and a blue-shifted double Gaussian which may indicate a partially obscured outflow. Weak narrow lines, together with the previously flat light curve, suggest that this object represents a dormant galactic nucleus which has recently been re-activated. Our time-series modelling of the Balmer lines suggests that this is connected to a disturbance in the disc morphology, and we speculate this could involve a sudden violent event such as a tidal disruption event involving the central supermassive black hole, though this cannot be confirmed, and given an estimated black hole mass of ≳ 107–108 M⊙ instabilities in an existing disc may be more likely. Although we find that the redshifts of AT2017bcc (z = 0.13) and G274296 (z > 0.42) are inconsistent, this event adds to the growing diversity of both nuclear transients and multimessenger contaminants.

Discovery of a Long-duration Superflare on a Young Solar-type Star EK Draconis with Nearly Similar Time Evolution for Hα and White-light Emissions

Abstract Young solar-type stars are known to show frequent “superflares,” which may severely influence the habitable worlds on young planets via intense radiation and coronal mass ejections. Here we report an optical spectroscopic and photometric observation of a long-duration superflare on the young solar-type star EK Draconis (50–120 Myr age) with the Seimei telescope and Transiting Exoplanet Survey Satellite. The flare energy 2.6 × 1034 erg and white-light flare duration 2.2 hr are much larger than those of the largest solar flares, and this is the largest superflare on a solar-type star ever detected by optical spectroscopy. The Hα emission profile shows no significant line asymmetry, meaning no signature of a filament eruption, unlike the only previous detection of a superflare on this star. Also, it did not show significant line broadening, indicating that the nonthermal heating at the flare footpoints is not essential or that the footpoints are behind the limb. The time evolution and duration of the Hα flare are surprisingly almost the same as those of the white-light flare, which is different from general M-dwarf (super-)flares and solar flares. This unexpected time evolution may suggest that different radiation mechanisms than general solar flares are predominant, such as: (1) radiation from (off-limb) flare loops and (2) re-radiation via radiative back-warming, in both of which the cooling timescales of flare loops could determine the timescales of Hα and white light.

The Viscosity Parameter for Late-type Stable Be Stars

Abstract Using hydrodynamic principles we investigate the nature of the disk viscosity following the parameterization by Shakura & Sunyaev adopted for the viscous decretion model in classical Be stars. We consider a radial viscosity distribution including a constant value, a radially variable α assuming a power-law density distribution, and isothermal disks, for a late-B central star. We also extend our analysis by determining a self-consistent temperature disk distribution to model the late-type Be star 1 Delphini, which is thought to have a nonvariable, stable disk as evidenced by Hα emission profiles that have remained relatively unchanged for decades. Using standard angular momentum loss rates given by Granada et al., we find values of α of approximately 0.3. Adopting lower values of angular momentum loss rates, i.e., smaller mass loss rates, leads to smaller values of α. The values for α vary smoothly over the Hα emitting region and exhibit the biggest variations nearest the central star within about five stellar radii for the late-type, stable Be stars.

Structure of accretion flows in the nova-like cataclysmic variable RW Tri

ABSTRACT We obtained photometric observations of the nova-like (NL) cataclysmic variable RW Tri and gathered all available AAVSO and other data from the literature. We determined the system parameters and found their uncertainties using the code developed by us to model the light curves of binary systems. New time-resolved optical spectroscopic observations of RW Tri were also obtained to study the properties of emission features produced by the system. The usual interpretation of the single-peaked emission lines in NL systems is related to the bi-conical wind from the accretion disc’s inner part. However, we found that the Hα emission profile is comprised of two components with different widths. We argue that the narrow component originates from the irradiated surface of the secondary, while the broader component’s source is an extended, low-velocity region in the outskirts of the accretion disc, located opposite to the collision point of the accretion stream and the disc. It appears to be a common feature for long-period NL systems – a point we discuss.

Spectroscopic Study of Be Star β Lyrae

We present the spectroscopic observation of β Lyrae, an interacting eclipsing binary, with orbital rotation period of 12.9 days, with one component known as the B-emission (Be) star. The primary star is a B6-B8II of 3 M⊙ and the secondary is a 13 M⊙ B0.5V star. The secondary star is embedded in the accretion disk produced by the infalling matter from the primary star, and this disk is estimated as the source of the emission lines. The observations were conducted at Bosscha Observatory, Lembang, Indonesia from May to August 2018, using 10” Meade LX-200R Telescope (D = 254 f/D = 9.84), equipped with a Littrow High Resolution Spectrograph (LHIRES) III, grating of 1200 grooves/mm yielding in the resolution of R∼5900, and CCD SBIG ST-402 XME camera with backfocus at 17.5 mm. Seeing during observation was estimated to be 2 arc seconds. During this period, we have obtained 15 spectra in various wavelength coverage, 4 spectra covering around λλ = 5779 – 6046 ÅÅ (typical S/N = 0.02), 1 spectrum covering around λλ = 6430.257 – 6694.434 ÅÅ (typical S/N = 0.06), and 10 spectra covering around λλ = 6487 – 6752 ÅÅ (typical S/N = 0.06). The observed spectra show Hα-emission profiles with V/R variation, He I 6678 Å with P-Cygni profiles, and He I 5876 Å with P-Cygni profiles. These variations are due to the fact that β Lyrae is a binary star system, and also it is suspected that another possible mechanism might be involved.

Frequency Analysis of a Potential SPB Star η Tau

In this study, five years of photometric data of η Tau obtained from the STEREO satellite between 2007 and 2011 are presented. The high-precision data are compared with the results derived from the spectroscopic findings to gain a better understanding of the Be phenomenon in the star. The spectroscopic data cover the same time interval as the photometric observations. η Tau displays a double peaked Hα emission profile in its spectra. In order to analyze this profile, the Hα emission lines are examined by measuring their equivalent widths and line intensities. As a result of the photometric and spectroscopic analyses, it is revealed that the frequency distribution and amplitude intensities of the star are different from those of a typical Be star. Based on its physical parameters such as temperature and luminosity values, it may be conclude that the star is a Slowly Pulsating B type emission star. On the other hand, the equivalent width values of the emission lines appear to be related to the oscillation frequencies and their amplitudes. This indicates that the photometric variations may be related to the environmental disc structure.Doğuş ÖZUYAR, dozuyar@ankara.edu.tr, ORCID: https://orcid.org/ 0000-0001-8544-0950

ASASSN-15nx: A Luminous Type II Supernova with a “Perfect” Linear Decline

Abstract We report a luminous Type II supernova, ASASSN-15nx, with a peak luminosity of mag that is between those of typical core-collapse supernovae and super-luminous supernovae. The post-peak optical light curves show a long, linear decline with a steep slope of 2.5 mag (100 day)−1 (i.e., an exponential decline in flux) through the end of observations at phase . In contrast, the light curves of hydrogen-rich supernovae (SNe II-P/L) always show breaks in their light curves at phase ∼100 day, before settling onto 56Co radioactive decay tails with a decline rate of about 1 mag (100 day)−1. The spectra of ASASSN-15nx do not exhibit the narrow emission-line features characteristic of Type IIn SNe, which can have a wide variety of light-curve shapes usually attributed to strong interactions with a dense circumstellar medium (CSM). ASASSN-15nx has a number of spectroscopic peculiarities, including a relatively weak and triangular-shaped Hα emission profile with no absorption component. The physical origin of these peculiarities is unclear, but the long and linear post-peak light curve without a break suggests a single dominant powering mechanism. Decay of a large amount of (M Ni = 1.6 ± 0.2 ) can power the light curve of ASASSN-15nx, and the steep light-curve slope requires substantial γ-ray escape from the ejecta, which is possible given a low-mass hydrogen envelope for the progenitor. Another possibility is strong CSM interactions powering the light curve, but the CSM needs to be sculpted to produce the unique light-curve shape and avoid producing SN IIn-like narrow emission lines.

A Study of the Hα Variability of Be Stars

Abstract This paper presents the results of 4 years of high-resolution spectral observations of 69 emission-line stars, 54 of them being newly discovered sources. We classified the stars on the basis of their position in the two-color IR diagram and some additional criteria: shape and width of the Hα profile, presence of He lines, proper motion and parallax, membership to open cluster and associations. Sixty of our targets turned out to be Be stars. We also found four late giants, four pre-MS stars, and one late dwarf. The Hα emission profiles of our Be stars range from single peaked to typical shell profiles that can also be highly asymmetric or single-peaked profiles with a narrow absorption core. The emission profiles appear almost constant with time or highly variable in intensity and in their V/R ratio. The detected long-term variability of the Hα emission is important for investigating the on/off switch phenomenon of Be stars. Our study led to an increase of the number of the emission-line stars of 16 open clusters.

Ω-slow Solutions and Be Star Disks

Abstract As the disk formation mechanism(s) in Be stars is(are) as yet unknown, we investigate the role of rapidly rotating radiation-driven winds in this process. We implemented the effects of high stellar rotation on m-CAK models accounting for the shape of the star, the oblate finite disk correction factor, and gravity darkening. For a fast rotating star, we obtain a two-component wind model, i.e., a fast, thin wind in the polar latitudes and an Ω-slow, dense wind in the equatorial regions. We use the equatorial mass densities to explore Hα emission profiles for the following scenarios: (1) a spherically symmetric star, (2) an oblate star with constant temperature, and (3) an oblate star with gravity darkening. One result of this work is that we have developed a novel method for solving the gravity-darkened, oblate m-CAK equation of motion. Furthermore, from our modeling we find that (a) the oblate finite disk correction factor, for the scenario considering the gravity darkening, can vary by at least a factor of two between the equatorial and polar directions, influencing the velocity profile and mass-loss rate accordingly, (b) the Hα profiles predicted by our model are in agreement with those predicted by a standard power-law model for following values of the line-force parameters: , and , and (c) the contribution of the fast wind component to the Hα emission line profile is negligible; therefore, the line profiles arise mainly from the equatorial disks of Be stars.

A catalog of early-type emission-line stars and Hα line profiles from LAMOST DR2

We present a catalog including 11 204 spectra of 10 436 early-type emission-line stars from LAMOST DR2, among which 9752 early-type emission-line spectra are newly discovered. For these early-type emission-line stars, we discuss the morphological and physical properties of their low-resolution spectra. In this spectral sample, the Hα emission profiles display a wide variety of shapes. Based on the Hα line profiles, these spectra are categorized into five distinct classes: single-peak emission, single-peak emission in absorption, double-peak emission, double-peak emission in absorption, and P-Cygni profiles. To better understand what causes the Hα line profiles, we divide these objects into four types from the perspective of physical classification, which include classical Be stars, Herbig Ae/Be stars, close binaries and spectra contaminated by HΠ regions. The majority of Herbig Ae/Be stars and classical Be stars are identified and separated using a (H-K, K-W1) color-color diagram. We also discuss 31 binary systems that are listed in the SIMBAD on-line catalog and identify 3600 spectra contaminated by HΠ regions after cross-matching with positions in the Dubout-Crillon catalog. A statistical analysis of line profiles versus classifications is then conducted in order to understand the distribution of Hα profiles for each type in our sample. Finally, we also provide a table of 172 spectra with Fe Π emission lines and roughly calculate stellar wind velocities for seven spectra with P-Cygni profiles.

THE B AND Be STATES OF THE STAR EM CEPHEUS

ABSTRACT We present 11 yr of high-resolution, spectroscopic observations for the star EM Cep. EM Cep switches between B and Be star states, as revealed by the level of Hα emission, but spends most of its time in the B star state. EM Cep has been considered to be an eclipsing, near-contact binary of nearly equal-mass B stars in order to reproduce regular photometric variations; however, this model is problematic due to the lack of any observed Doppler shift in the spectrum. Our observations confirm that there are no apparent Doppler shifts in the wide spectral lines Hα and He i λ6678 in either the B or Be star states. The profiles of He i λ6678 typically exhibited a filled-in absorption core, but we detected weak emission in this line during the highest Be state. Given the lack of observed Doppler shifts, we model EM Cep as an isolated Be star with a variable circumstellar disk. We can reproduce the observed Hα emission profiles over the 11 yr period reasonably well with disk masses on the order of in the Be state with the circumstellar disk seen at an inclination of 78° to the line of sight. From a disk ejection episode in 2014, we estimate a mass-loss rate of . The derived disk density parameters are typical of those found for the classical Be stars. We therefore suggest that the EM Cep is a classical Be star and that its photometric variations are the result of Cep or nonradial pulsations.

Spatially resolved kinematic observations of the planetary nebulae Hen 3-1333 and Hen 2-113

Abstract We have performed integral field spectroscopy of the planetary nebulae Hen 3-1333 (PNG332.9−09.9) and Hen 2-113 (PNG321.0+03.9), which are unusual in exhibiting dual-dust chemistry and multipolar lobes but also ionized by late-type [WC 10] central stars. The spatially resolved velocity distributions of the Hα emission line were used to determine their primary orientations. The integrated Hα emission profiles indicate that Hen 3-1333 and Hen 2-113 expand with velocities of ∼32 and 23 km s−1, respectively. The Hubble Space Telescope observations suggest that these planetary nebulae have two pairs of tenuous lobes extending upwardly from their bright compact cores. From three-dimensional geometric models, the primary lobes of Hen 3-1333 and Hen 2-113 were found to have inclination angles of about −30° and 40° relative to the line of sight, and position angles of −15° and 65° measured east of north in the equatorial coordinate system, respectively.

New insights on Be shell stars from modelling their Hα emission profiles

AbstractBe shell stars are believed to be ordinary Be stars seen edge-on, which makes them particularly desirable objects for study since the uncertainty in the inclination of the rotation axis is largely eliminated. We have recently modelled high resolution Hα spectroscopic observations for eight Be shell stars, using the non-local thermodynamical equilibrium radiative transfer codeBedisk(Sigut & Jones 2007) and the new spectral synthesis packageBeray(Sigut 2011). Generally, we confirm that these systems are oriented at high inclination angles, although we find that they are not necessarily as close to edge-on as initially expected.

Over-ablation and deflection of hydrogen pellets injected into neutral beam injection heated plasmas in the Large Helical Device

During hydrogen pellet injection experiments in the Large Helical Device (LHD), over-ablation caused by fast ions (due to tangential neutral beam injection (NBI) heating at 150–180 keV beam energy) is shown to dominate the measured penetration depths. The neutral gas and plasma shielding model, including the interaction of the pellet with fast ions, is applied, and its predictions are shown to agree well with the measured Hα emission profiles. The toroidal deflection of the pellet trajectories observed in the direction of beam injection is reproduced by the model when unbalanced ablation on the two sides of the pellet is included. The attenuation of the fast-ion and electron heat fluxes entering the ablation cloud is examined, showing that the high-energy part of the fast-ion distribution function is responsible for the high ablation rates, and that the thermal electron population is not the dominant ablating species. An analytical scaling for the balanced NBI condition is derived, which reasonably reproduces the measured penetration depths included in the LHD database. In the LHD, for given pellet parameters and beam energy, the fast-ion density is shown to be the major parameter affecting the experimental penetration.

Dynamical processes in the June 26, 1999 flare

The evolutionary and spatial characteristics of the motions in the flaring chromosphere of a 2B/M2.3 flare are investigated by analyzing the asymmetry in the Hα profiles. The possibility of reconciling the results of observations with the theory of chromospheric evaporation is considered. The spectroscopic Hα observations of the flare performed with the KG-2 CrAO coronagraph with a temporal resolution of 5–10 s and a spatial resolution as high as 1 arcsec cover all stages of flare development. The following results have been obtained: (1) The Hα profile asymmetry is a general characteristic of the flare emission irrespective of its intensity and its belonging to different structural features and phases of flare development. (2) Most of the Hα emission profiles in flare regions exhibit a red asymmetry. However, a blue asymmetry was observed in small local regions at all stages of flare development. (3) A red asymmetry that appeared before the onset of the impulsive phase and persisted after its end was observed at the sites of main energy release, i.e., the energy source responsible for the dynamical processes in the flare came into operation earlier and existed longer than the HXR emission. (4) The asymmetry pattern changed with flare phase: the red wing intensity dominated in the pre-impulsive phase and at the onset of the impulsive and gradual phases (while the line core was unshifted or slightly shifted). At the maximum of the impulsive phase, the nearly symmetric profiles with extended wings were redshifted as a whole, i.e., the entire emitting volume moved down with a velocity of several tens of km/s. This type of asymmetry cannot be explained by the dynamical model of chromospheric condensation (Canfield and Gayley 1987). (5) The Hα profiles show no evidence of chromospheric heating by a beam of nonthermal electrons during the impulsive phase (Canfield et al. 1984). (6) The lifetime of the downflows and the change in their velocities with time are inconsistent with the dynamical model of chromospheric condensation (Fisher 1989). (7) The morphological features of the velocity field are also inconsistent with the theory of chromospheric evaporation, because the highest differently directed velocities were detected at the flare loop tops, not at the sites of main energy release. We conclude that the investigated flare shows spectral features that are inconsistent with the standard chromospheric evaporation model.

Infrared Excess in the Be Star δ Scorpii

ABSTRACTWe present infrared photometric observations of the Be binary system δ Scorpii obtained in 2006. The J, H, and K magnitudes are the same within the errors compared to observations taken 10 months earlier. We derive the infrared excess from the observation and compare this to the color excess predicted by a radiative equilibrium model of the primary star and its circumstellar disk. We use a non-LTE computational code to model the gaseous envelope concentrated in the star’s equatorial plane and calculate the expected spectral energy distribution and Hα emission profile of the star with its circumstellar disk. Using the observed infrared excess of δ Sco, as well as Hα spectroscopy bracketing the IR observations in time, we place constraints on the radial density distribution in the circumstellar disk. Because the disk exhibits variability in its density distribution, this work will be helpful in understanding its dynamics.

Modeling of Emission Signatures of Massive Black Hole Binaries. I. Methods

We model the electromagnetic signatures of massive black hole binaries (MBHBs) with an associated gas component. The method comprises numerical simulations of relativistic binaries and gas coupled with calculations of the physical properties of the emitting gas. We calculate the UV/X-ray and the Hα light curves and the Hα emission profiles. The simulations are carried out with a modified version of the parallel tree SPH code Gadget. The heating, cooling, and radiative processes are calculated for two different physical scenarios, where the gas is approximated as a blackbody or a solar metallicity gas. The calculation for the solar metallicity scenario is carried out with the photoionization code Cloudy. We focus on subparsec binaries that have not yet entered the gravitational radiation phase. The results from the first set of calculations, carried out for a coplanar binary and gas disk, suggest that there are pronounced outbursts in the X-ray light curve during pericentric passages. If such outbursts persist for a large fraction of the lifetime of the system, they can serve as an indicator of this type of binary. The predicted Hα emission line profiles may be used as a criterion for selection of MBHB candidates from existing archival data. The orbital period and mass ratio of a binary may be inferred after carefully monitoring the evolution of the Hα profiles of the candidates. The discovery of subparsec binaries is an important step in understanding of the merger rates of MBHBs and their evolution toward the detectable gravitational wave window.

Joint Hα and X‐Ray Observations of Massive X‐Ray Binaries. I. The B Supergiant System LS I +65 010 = 2S 0114+650

We report on a 3 yr spectroscopic monitoring program of the Hα emission in the massive X-ray binary LS I +65 010 = 2S 0114+650, which consists of a B supergiant and a slowly rotating X-ray pulsar. We present revised orbital elements that yield a period of P = 11.5983 ± 0.0006 days and confirm that the orbit has a nonzero eccentricity e = 0.18 ± 0.05. The Hα emission profile is formed in the base of the wind of the B supergiant primary, and we show how this spectral feature varies on timescales that are probably related to the rotational period of the B supergiant. We also examine the X-ray fluxes from the Rossi X-ray Timing Explorer All-Sky Monitor instrument, and we show that the X-ray orbital light curve has a maximum at periastron and a minimum at the inferior conjunction of the B supergiant. We also show that the wind emission strength and the high-energy X-ray flux appear to vary in tandem on timescales of approximately 1 yr.

Three-dimensional transport of neutral particles in the CHS edge region

We used Monte Carlo simulation code DEGAS and studied the neutral particle behavior in the Compact Helical System (CHS) three-dimensionally. In contrast to other helical devices, the CHS plasma in the standard configuration has contact with the inner vacuum vessel wall like the material limiter used in many Tokamaks and the neutral recycling becomes dominant there. As the intensity of neutral recycling changes also along toroidal direction, we extended our previous simulation model geometry three-dimensionally and compared the results of these models. We found the variation of the gap between the vacuum wall and main plasma enhanced toroidal transport of hydrogen molecules and atoms. As the formation of the edge transport barrier (EBT) discovered recently in CHS is characterized by a clear drop in Hα emissions, it is interesting to study the relationship with the profile of atomic/molecular hydrogen and the Hα emission profile. We estimated emission not only from excited hydrogen atoms but also from dissociated molecules with a collisional radiation model. We found that our Hα detector signal in CHS mostly came from excited atoms and that the emission profile largely changed with the ETB formation.

H α measurements and neutral particle transport in Heliotron J

A multichannel system of the Hα-line emission detector is developed in order to investigate the neutral particle transport in the Heliotron J plasma. The application of a multianode photomultiplier tube to the filter measurement system enables us to observe the Hα emission profile with 32 chords. The absolute calibration with a standard lamp is performed and the cross-talk between each of the adjoining channels is evaluated to be less than 6%, while the photomultiplier tube has a typical cross-talk of 3% in nominal value. The temporal and spatial profiles of the Hα emission are measured in detail in the plasma breakdown by electron cyclotron heating (ECH). The Hα emission profile in the ECH plasma is calculated by the Monte Carlo simulation using a three-dimensional mesh model. The fueling rates of the wall recycling and the gas puffing are estimated by means of the simulation and the measurement.