Search

Hydrogen Balmer lines are commonly used as spectroscopic effective temperature diagnostics of late-type stars. However, reliable inferences require accurate model spectra, and the absolute accuracy of classical methods that are based on one-dimensional (1D) hydrostatic model atmospheres and local thermodynamic equilibrium (LTE) is still unclear. To investigate this, we carry out 3D non-LTE calculations for the Balmer lines, performed, for the first time, over an extensive grid of 3D hydrodynamic STAGGER model atmospheres. For Hα, Hβ, and Hγ we find significant 1D non-LTE versus 3D non-LTE differences (3D effects): the outer wings tend to be stronger in 3D models, particularly for Hγ, while the inner wings can be weaker in 3D models, particularly for Hα. For Hα, we also find significant 3D LTE versus 3D non-LTE differences (non-LTE effects): in warmer stars (Teff ≈ 6500 K) the inner wings tend to be weaker in non-LTE models, while at lower effective temperatures (Teff ≈ 4500 K) the inner wings can be stronger in non-LTE models; the non-LTE effects are more severe at lower metallicities. We test our 3D non-LTE models against observations of well-studied benchmark stars. For the Sun, we infer concordant effective temperatures from Hα, Hβ, and Hγ; however the value is too low by around 50 K which could signal residual modelling shortcomings. For other benchmark stars, our 3D non-LTE models generally reproduce the effective temperatures to within 1σ uncertainties. For Hα, the absolute 3D effects and non-LTE effects can separately reach around 100 K, in terms of inferred effective temperatures. For metal-poor turn-off stars, 1D LTE models of Hα can underestimate effective temperatures by around 150 K. Our 3D non-LTE model spectra are publicly available, and can be used for more reliable spectroscopic effective temperature determinations. [ABSTRACT FROM AUTHOR]

We discuss the rest-frame ultraviolet (UV) emission line spectra of a large (∼100) sample of low luminosity redshift z ∼ 3.1 Lyman alpha emitters (LAEs) drawn from a Subaru imaging survey in the SSA22 survey field. Our earlier work based on smaller samples indicated that such sources have high [O iii]/[O ii] line ratios possibly arising from a hard ionizing spectrum that may be typical of similar sources in the reionization era. With optical spectra secured from VLT/VIMOS, we re-examine the nature of the ionizing radiation in a larger sample using the strength of the high ionization diagnostic emission lines of Ciii]λ1909, Civλ1549, Heiiλ1640, and O iii]λλ1661, 1666 Å in various stacked subsets. Our analysis confirms earlier suggestions of a correlation between the strength of Ly α and Ciii] emission and we find similar trends with broad-band UV luminosity and rest-frame UV colour. Using various diagnostic line ratios and our stellar photoionization models, we determine both the gas phase metallicity and hardness of the ionization spectrum characterized by ξion – the number of Lyman continuum photons per UV luminosity. We confirm our earlier suggestion that ξion is significantly larger for LAEs than for continuum-selected Lyman break galaxies, particularly for those LAEs with the faintest UV luminosities. We briefly discuss the implications for cosmic reionization if the metal-poor intensely star-forming systems studied here are representative examples of those at much higher redshift. [ABSTRACT FROM AUTHOR]

Post-starburst galaxies can be identified via the presence of prominent Hydrogen Balmer absorption lines in their spectra. We present a comprehensive study of the origin of strong Balmer lines in a volume-limited sample of 189 galaxies with 0.01 < z < 0.05, $\log ({\it M}_{\star }/{\it M}_{{\odot }})>9.5$ and projected axial ratio b/a > 0.32. We explore their structural properties, environments, emission lines, and star formation histories, and compare them to control samples of star-forming and quiescent galaxies, and simulated galaxy mergers. Excluding contaminants, in which the strong Balmer lines are most likely caused by dust-star geometry, we find evidence for three different pathways through the post-starburst phase, with most events occurring in intermediate-density environments: (1) a significant disruptive event, such as a gas-rich major merger, causing a starburst and growth of a spheroidal component, followed by quenching of the star formation (70 per cent of post-starburst galaxies at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$ and 60 per cent at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$ ); (2) at $9.5<\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})<10.5$ , stochastic star formation in blue-sequence galaxies, causing a weak burst and subsequent return to the blue sequence (30 per cent); (3) at $\log (\mbox{{$M$}}_{\star }/\mbox{{$M$}}_{{\odot }})>10.5$ , cyclic evolution of quiescent galaxies which gradually move towards the high-mass end of the red sequence through weak starbursts, possibly as a result of a merger with a smaller gas-rich companion (40 per cent). Our analysis suggests that active galactic nuclei (AGNs) are 'on' for $50\hbox{ per cent}$ of the duration of the post-starburst phase, meaning that traditional samples of post-starburst galaxies with strict emission-line cuts will be at least $50\hbox{ per cent}$ incomplete due to the exclusion of narrow-line AGNs. [ABSTRACT FROM AUTHOR]

Our aim is to understand the role of the environment in the quenching of star formation of galaxies located in the infall cluster region of Abell 85 (A85). This is achieved by studying the post-starburst galaxy population as tracer of recent quenching. By measuring the equivalent width (EW) of the [O ii] and Hδ spectral lines, we classify the galaxies into three groups: passive (PAS), emission line (EL), and post-starburst (PSB) galaxies. The PSB galaxy population represents ${\sim } 4.5\hbox{ per cent}$ of the full sample. Dwarf galaxies (Mr > −18.0) account for ${\sim } 70 {\rm -} 80\hbox{ per cent}$ of PSBs, which indicates that most of the galaxies undergoing recent quenching are low-mass objects. Independently of the environment, PSB galaxies are disc-like objects with g − r colour between the blue ELs and the red PAS ones. The PSB and EL galaxies in low-density environments show similar luminosities and local galaxy densities. The dynamics and local galaxy density of the PSB population in high-density environments are shared with PAS galaxies. However, PSB galaxies inside A85 are at shorter clustercentric radius than PAS and EL ones. The value of the EW(Hδ) is larger for those PSBs closer to the cluster centre. We propose two different physical mechanisms producing PSB galaxies depending on the environment. In low-density environments, gas-rich minor mergers or accretions could produce the PSB galaxies. For high-density environments like A85, PSBs would be produced by the removal of the gas reservoirs of EL galaxies by ram-pressure stripping when they pass near the cluster centre. [ABSTRACT FROM AUTHOR]

Stars that exhibit a B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including the presence of Balmer lines in emission, forbidden lines and strong infrared excess due to dust. Observations of emission lines indicate illumination by an ultraviolet ionizing source, which is key to understanding the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from the Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and the correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including light absorption by the disc, pulsations, luminous blue variable type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is present not only in the disc but also above its plane. The flux and line variability is consistent with a two-component model of a circumstellar environment composed of a dense disc and an ionized envelope. Observations of B[e] supergiants show that many of these stars have nearly the same luminosity, about 1.9 × 105 L⊙, and similar effective temperatures. [ABSTRACT FROM AUTHOR]

Supernova (SN) 2016bdu is an unusual transient resembling SN 2009ip. SN 2009ip-like events are characterized by a long-lasting phase of erratic variability that ends with two luminous outbursts a few weeks apart. The second outburst is significantly more luminous (about 3mag) than the first. In the case of SN 2016bdu, the first outburst (Event A) reached an absolute magnitude Mr ≈ -15.3 mag, while the second one (Event B) occurred over one month later and reached Mr ≈ -18 mag. By inspecting archival data, a faint source at the position of SN 2016bdu is several times in the past few years. We interpret these detections as signatures of a phase of erratic variability, similar to that experienced by SN 2009ip between 2008 and mid-2012, and resembling the currently observed variability of the luminous blue variable SN 2000ch in NGC 3432. Spectroscopic monitoring of SN 2016bdu during the second peak initially shows features typical of an SN IIn. One month after the Event B maximum, the spectra develop broad Balmer lines with P Cygni profiles and broad metal features. At these late phases, the spectra resemble those of a typical Type II SN. All members of this SN 2009ip-like group are remarkably similar to the Type IIn SN 2005gl. For this object, the claim of a terminal SN explosion is supported by the disappearance of the progenitor star. While the similarity with SN 2005gl supports a genuine SN explosion scenario for SN 2009ip-like events, the unequivocal detection of nucleosynthesized elements in their nebular spectra is still missing. [ABSTRACT FROM AUTHOR]

This paper presents the results of the investigation of plasma electrolytic oxidation (PEO) of hafnium. Atoms ionized during the PEO micro-discharging were identified using optical emission spectroscopy. The spectral line shape analysis of the hydrogen Balmer line H β indicated the presence of two types of micro-discharges characterized by electron number densities of around 2.5·10 21 m − 3 and 1.3·10 22 m − 3 . Scanning electron microscopy and X-ray diffraction were employed to investigate surface morphology and phase composition of the PEO coatings obtained. The coatings were crystalline and composed of monoclinic HfO 2 . Diffuse reflectance spectroscopy has shown that HfO 2 coatings have a broad absorption band in the range from 200 nm to 400 nm. Optical band gap of HfO 2 coatings was around 5.4 eV, as estimated from absorption spectra. Photoluminescence measurements show that HfO 2 coatings have broad emission band in the visible region, with a maximum at around 480 nm. The highest photoluminescence was obtained for the excitation wavelength of 270 nm. Intensity of photoluminescence increased with PEO time and is related to an increase of oxygen vacancy defects in HfO 2 coatings formed during the process. [ABSTRACT FROM AUTHOR]

We present the results of our spectroscopic study of the dwarf nova SS Cyg, using Roche tomography to map the stellar surface and derive the system parameters. Given that this technique takes into account the inhomogeneous brightness distribution on the surface of the secondary star, our derived parameters are (in principle) the most robust yet found for this system. Furthermore, our surface maps reveal that the secondary star is highly spotted, with strongly asymmetric irradiation on the inner hemisphere. Moreover, by constructing Doppler tomograms of several Balmer emission lines, we find strong asymmetric emission from the irradiated secondary star, and an asymmetric accretion disc that exhibits spiral structures. [ABSTRACT FROM AUTHOR]

We use the Balmer decrements of the broad-line regions (BLRs) and narrow-line regions (NLRs) of active galactic nuclei (AGNs) as reddening indicators to investigate the location of the dust for four samples of AGNs with reliable estimates of the NLR contribution to the Balmer lines. Intercomparison of the NLR and BLR Balmer decrements indicates that the reddening of the NLR sets a lower limit to the reddening of the BLR. Almost no objects have high NLR reddening but low BLR reddening. The reddening of the BLR is often substantially greater than the reddening of the NLR. The BLR reddening is correlated with the equivalent widths of [O III] lines and the intensity of the [O III] lines relative to broad Hβ. We find these relationships to be consistent with the predictions of a simple model where the additional dust reddening the BLR is interior to the NLR. We thus conclude that the dust causing the additional reddening of the accretion disc and BLR is mostly located at a smaller radius than the NLR. [ABSTRACT FROM AUTHOR]

We report the detection of high-amplitude X-ray flaring of the AGN HE 1136-2304, which is accompanied by a strong increase in the flux of the broad Balmer lines, changing its Seyfert type from almost type 2 in 1993 down to 1.5 in 2014. HE 1136-2304 was detected by the XMM-Newton slew survey at >10 times the flux it had in the ROSAT all-sky survey, and confirmed with Swift follow-up after increasing in X-ray flux by a factor of ~30. Optical spectroscopy with SALT shows that the AGN has changed from a Seyfert 1.95 to a Seyfert 1.5 galaxy, with greatly increased broad line emission and an increase in blue continuum AGN flux by a factor of >4. The X-ray spectra from XMM-Newton and NuSTAR reveal moderate intrinsic absorption and a high energy cutoff at ~100 keV. We consider several different physical scenarios for a flare, such as changes in obscuring material, tidal disruption events, and an increase in the accretion rate. We find that the most likely cause of the increased flux is an increase in the accretion rate, although it could also be due to a change in obscuration. [ABSTRACT FROM AUTHOR]

The JET Neutral Beam Injection (NBI) system is the most powerful neutral beam plasma heating system currently operating. Optical Interlocks were installed on the beam lines in 2011 for the JET Enhancement Project 2 (EP2), when the heating power was increased from 23 MW to 34 MW. JET NBI has two beam lines. Each has eight positive ion injectors operating in deuterium at 80 kV–125 kV (accelerator voltage) and up to 65 A (beam current). Heating power is delivered through two ducts where the central power density can be more than 100 MW/m 2 . In order to deliver this safely, the beam line pressure should be below 2 × 10 −5 mbar otherwise the power load on the duct from the re-ionised fraction of the beam is excessive. The new Optical Interlock monitors the duct pressure by measuring the Balmer- α beam emission (656 nm). This is proportional to the instantaneous beam flux and the duct pressure. Light is collected from a diagnostic window and focused into 1-mm diameter fibres. The Doppler shifted signal is selected using an angle-tuned interference filter. The light is measured by a photo-multiplier module with a logarithmic amplifier. The interlock activation time of 2 ms is sufficient to protect the system from a fully re-ionised beam—a significant improvement on the previous interlock. The dynamic range is sufficient to see bremsstrahlung emission from JET plasma and not saturate during plasma disruptions. For high neutron flux operations the optical fibres within the biological shield can be annealed to 350 °C. A self-test is possible by illuminating the diagnostic window with a test lamp and measuring the back scatter. We demonstrate an important technology for the protection of high power neutral heating beams and present the design and operational results. [ABSTRACT FROM AUTHOR]

Context. Searches for magnetic fields in white dwarfs have clarified both the frequency of occurrence and the global structure of the fields found down to field strengths of the order of 500 kG. Below this level, the situation is still very unclear. Aims. We are engaged in a project to find and study the weakest magnetic fields that are detectable in white dwarfs, in order to empirically determine how the frequency of occurrence and the structure of fields present changes with field strength. In this paper we report the successful testing of a very sensitive method of longitudinal field detection in DA white dwarfs. We use this method to carry out an extremely sensitive search for magnetism in the bright white dwarf 40 Eri B. Methods. The method of field measurement we use is to measure, at high spectral resolution, the polarisation signal V/I of the narrow non-LTE line core in Hα in DA stars. This small feature provides a much higher amplitude polarisation signal than the broad Balmer line wings. We test the usefulness of this technique by searching for a weak magnetic field in 40 Eri B. Results. One hour of observation of I and V Stokes components of the white dwarf 40 Eri B using ESPaDOnS at the CFHT is found to provide a standard error of measurement of the mean longitudinal magnetic field of about 85 G. This is the smallest standard error of field measurement ever obtained for a white dwarf. The non-detections obtained are generally consistent with slightly less accurate measurements of 40 Eri B obtained with ISIS at the WHT and the Main Stellar Spectrograph at SAO, in order to provide comparison standards for the new method. These further measurements allow us to make a quantitative comparison of the relative efficiencies of low-resolution spectropolarimetery (using most or all of the Balmer lines) with the new method (using only the core of Hα). Conclusions. The new method of field detection reaches the level of sensitivity that was expected. It appears that for suitable DA stars, about the same field uncertainties can be reached with ESPaDOnS on the CFHT, in a given integration time, as with FORS on an 8-m telescope, and uncertainties are a factor of two better than with low-resolution spectropolarimetry with other 4-6-m class telescopes. However, even with this extraordinary sensitivity, there is no clear indication of the presence of any magnetic field in 40 Eri B above the level of about 250 G. [ABSTRACT FROM AUTHOR]

We restudy the issue of cross-correlations between broad-line and jet emission variations, and aim to locate the position of a radio (and gamma-ray) emitting region in a jet of active galactic nuclei. Considering the radial profiles of the radius and number density of clouds in a spherical broad-line region (BLR), we derive new formulae connecting the jet-emitting position Rjet to the time lag τob between broad-line and jet emission variations, and the BLR radius. Also, formulae are derived for a disc-like BLR and a spherical shell BLR. The modelindependent flux randomization/random subset selection method is used to estimate τob. For 3C 120, positive lags of about 0.3 yr are found between the 15 GHz emission and the Hβ, Hγ and He II λ4686 lines, including broad-line data in a newly published paper, indicating that the line variations lead the 15 GHz ones. Each of the broad-line light curves corresponds to a radio outburst. Rjet = 1.1-1.5 parsec (pc) is obtained for 3C 120. For 3C 273, a common feature of negative time lags is found in the cross-correlation functions between light curves of radio emission and the Balmer lines, as well as Lyα λ1216 and CIV λ1549 lines. Rjet = 1.0-2.6 pc is obtained for 3C 273. The estimated Rjet is comparable for 3C 120 and 3C 273, and the gamma-ray-emitting positions will be within ∼1-3 pc from the central engines. Comparisons show that the cloud number density and radius radial distributions and the BLR structures have only negligible effects on Rjet. [ABSTRACT FROM AUTHOR]

Context. Synthetic model atmosphere calculations are still the most commonly used tool when determining precise stellar parameters and stellar chemical compositions. Besides three-dimensional models that consistently solve for hydrodynamic processes, one dimensional models that use an approximation for convective energy transport play the major role. Aims. We use modern Balmer-line formation theory as well as spectral energy distribution (SED) measurements for the Sun and Procyon to calibrate the model parameter that describes the effciency of convection in our 1D models. Convection was calibrated over a significant range in parameter space, reaching from F-K along the main sequence and sampling the turno and giant branch over a wide range of metallicities. This calibration was compared to theoretical evaluations and allowed an accurate modeling of stellar atmospheres. Methods. We used Balmer-line fitting and SED fits to determine the convective effciency parameter α. Both methods are sensitive to the structure and temperature stratification of the deeper photosphere. Results. While SED fits do not allow a precise determination of the convective parameter for the Sun and Procyon, they both favor values significantly higher than 1.0. Balmer-line fitting, which we find to be more sensitive, suggests that the convective effciency parameter α is ≈2.0 for the main sequence and quickly decreases to ≈1.0 for evolved stars. These results are highly consistent with predictions from 3D models. While the values on the main sequence fit predictions very well, measurements suggest that the decrease of convective effciency as stars evolve to the giant branch is more dramatic than predicted by models. [ABSTRACT FROM AUTHOR]

We introduce Coronal-Line Forest active galactic nuclei (CLiF AGN), AGN which have a rich spectrum of forbidden high-ionization lines (FHILs, e.g. [Fe VII], [Fe X] and [Ne V]), as well as relatively strong narrow (~300 km s-1) Ha emission when compared to the other Balmer transition lines. We find that the kinematics of the CLiF emitting region are similar to those of the forbidden low-ionization emission-line (FLIL) region. We compare emission line strengths of both FHILs and FLILs to CLOUDY photoionization results and find that the CLiF emitting region has higher densities (104.5 < nH < 107.5 cm-3) when compared to the FLIL emitting region (103.0 < nH < 104.5 cm-3). We use the photoionization results to calculate the CLiF regions radial distances (0.04 < RCLiF < 32.5 pc) and find that they are comparable to the dust grain sublimation distances (0.10 < RSUB < 4.3 pc). As a result, we suggest that the inner torus wall is the most likely location of the CLiF region, and the unusual strength of the FHILs is due to a specific viewing angle giving a maximal view of the far wall of the torus without the continuum being revealed. [ABSTRACT FROM AUTHOR]

In this paper, the addition of Ar to H2 is experimentally investigated. This paper primarily aims to observe the effects that this addition has on the intensity of hydrogen emission lines in a glow discharge mixture. The total pressure was 3 torr, at a power level of 3.9 W. Optical emission spectroscopy was used for plasma characterization, and the principal species observed were H \gamma (434 nm), H \vphantom {RRR{\beta }} (486.1 nm), H \alpha (656.3 nm), and H2 (603.1 nm), and Ar I (750.5 nm), Ar I (763.5 nm), and Ar I (811.6 nm). The electron temperature and ion density were determined by a double Langmuir probe. The electron temperature was found to be in the range of 2.5–6.5 eV, and the ion concentration was on the order of 10^9 cm ^-3 . [ABSTRACT FROM PUBLISHER]

We carried out high-sensitivity spectro-polarimetric observations of the central star of the Red Rectangle protoplanetary nebula with the aim of constraining the mechanism that gives its biconical shape. The stellar light of the central binary system is linearly polarised since it is scattered on the dust particles of the nebula. Surprisingly, the linear polarisation in the continuum is aligned with one of the spikes of the biconical outflow. Also, the observed Balmer lines, as well as the Ca ii K lines, are polarised. These observational constraints are used to confirm or reject current theoretical models for the shaping mechanism of the Red Rectangle. We propose that the observed polarisation is not very likely to be generated by a uniform biconical stellar wind. Also, the hypothesis of a precessing jet does not completely match observations since it requires a larger aperture jet than for the nebula. [ABSTRACT FROM AUTHOR]

Here we present a new method for subtracting the Balmer pseudocontinuum in the UV part of type 1 AGN spectra. We calculate the intensity of the Balmer pseudocontinuum using the prominent Balmer lines in AGN spectra. We apply the model on a sample of 293 type 1 AGNs from SDSS database, and found that our model of Balmer pseudocontinuum + power law continuum very well fits the majority of AGN spectra from the sample, while in ∼ 15% of AGNs, the model fits reasonable the UV continuum, but a discrepancy between the observed and fitted spectra is noted. Some of the possible reasons for the discrepancy may be a different value for the optical depth in these spectra than used in our model or the influence of the intrinsic reddening. [ABSTRACT FROM AUTHOR]

It is becoming clear that we can define two different types of nearby AGN belonging to the Seyfert 1 class (S1), on the basis of the match of the intensities of their Broad Balmer Lines (BBL) with the Boltzmann Plots (BP). These two types of S1 galaxies, that we call BP-S1 and NoBP-S1, are characterized, in first approximation, by Broad Line Regions (BLR) with different structural and physical properties. In this communication, we show that these features can be well pointed out by a multi-wavelength analysis of the continuum and of the broad recombination Hydrogen lines, that we carry out on a sample of objects detected at optical and X-ray frequencies. The investigation is addressed to verify whether BP-S1 are the ideal candidates for the study of the kinematical and structural properties of the BLR, in order to derive reliable estimates of the mass of their central engine and to constrain the properties of their nuclear continuum spectrum. [ABSTRACT FROM AUTHOR]

Aims. The study is aimed at discovering new objects with the B[e] phenomenon in the Large Magellanic Cloud. Methods. We report medium-resolution optical spectroscopic observations of two newly found (ARDB54 and NOMAD0181-0125572) and two previously known (Hen S-59 and Hen S-137) supergiants with the B[e] phenomenon in the Large Magellanic Cloud. The observations were obtained with the GMOS spectrograph at the southern Gemini telescope. Results. The optical spectra and the fundamental parameters of ARDB54 and NOMAD0181-0125572 are presented for the first time. We found that the Balmer line profiles of Hen S-59 and Hen S-137 were different from those observed in their spectra nearly 20 years ago. We suggest a higher effective temperature and luminosity for both objects. With the new fundamental parameters, the lowest luminosity for known supergiants with the B[e] phenomenon in the Magellanic Clouds is higher that previously thought (log L/L⊙ ~ 4.5 instead of 4.0). The object Hen S-59 may be a binary system based on its UV excess, variable B - V color-index and radial velocity of emission lines, and periodically variable I-band brightness. [ABSTRACT FROM AUTHOR]

Context. Though Lyα emission is one of the most used tracers of massive star formation at high redshift, it is strongly affected by neutral gas radiation transfer effects. A correct understanding of these effects is required to properly quantify the star formation rate along the history of the Universe. Aims. We aim to parameterize the escape of Lyα photons as a function of the galaxy properties, in order to properly calibrate the Lyα luminosity as a tracer of star formation intensity at any age of the Universe. Methods. We have embarked on a program to study the properties of the Lyα emission (spectral profile, spatial distribution, relation to Balmer lines intensity,...) in a number of starburst galaxies in the Local Universe. The study is based on Hubble Space Telescope spectroscopic and imaging observations at various wavelengths, X-ray data, and ground-based spectroscopy, complemented with the use of evolutionary population synthesis models. Results. We present here the results obtained for one of those sources, IRAS 08339+6517, a strong Lyα emitter in the Local Universe, which is undergoing an intense episode of massive star formation. We have characterized the properties of the starburst, which transformed 1.4 × 108 M⊙ of gas into stars around 5−6 Myr ago. The mechanical energy released by the central super stellar cluster (SSC), located in the core of the starburst, has created a cavity devoid of gas and dust around it, leaving a clean path through which the UV continuum of the SSC is observed, with almost no extinction. While the average extinction affecting the stellar continuum is significantly larger out of the cavity, with E(B − V) = 0.15 on average, we have not found any evidence for regions with very large extinctions, which could be hiding some young, massive stars not contributing to the global UV continuum. The observed soft and hard X-ray emissions are consistent with this scenario, being originated by the interstellar medium heated by the release of mechanical energy in the first case, and by a large number of active high-mass X-ray binaries (HMXBs) in the second. In addition to the central compact emission blob, we have identified a diffuse Lyα emission component smoothly distributed over the whole central area of IRAS 08339+6517. This diffuse emission is spatially decoupled from the UV continuum, the Hα emission, or the Hα/Hβ ratio. Both locally and globally, the Lyα/Hα ratio is lower than the Case B predictions, even after reddening correction, with an overall Lyα escape fraction of only 4%. Conclusions. We conclude that in IRAS 08339+6517 the Lyα photons resonantly scattered by an outflowing shell of neutral gas are being smoothly redistributed over the whole central area of the galaxy. Their increased probability of being destroyed by dust would explain the low Lyα escape fraction measured. In any case, in the regions where the diffuse Lyα emission shows the largest Lyα/Hα ratios, no additional sources of Lyα emission are required, like ionization by hot plasma as proposed for Haro 2, another galaxy in our sample. These results stress again the importance of a proper correction of scattering and transfer effects when using Lyα to derive the star formation rate in high-redshift galaxies. [ABSTRACT FROM AUTHOR]

Context. Observation of Balmer lines from the region around the forward shock of supernova remnants (SNRs) may provide valuable information on the shock dynamics and the efficiency of particle acceleration at the shock. Aims. We calculated the Balmer line emission and the shape of the broad Balmer line for parameter values suitable for SNR RCW86 (G315.4 - 2.3) as a function of the cosmic-ray (CR) acceleration efficiency and of the level of thermal equilibration between electrons and protons behind the shock. This calculation aims at using the width of the broad Balmer-line emission to infer the CR acceleration efficiency in this remnant. Methods. We used the recently developed non linear theory of diffusive shock-acceleration in the presence of neutrals. The semi-analytical approach we developed includes a description of magnetic field amplification as due to resonant streaming instability, the dynamical reaction of accelerated particles and the turbulent magnetic field on the shock, and all channels of interaction between neutral hydrogen atoms and background ions that are relevant for the shock dynamics. Results. We derived the CR acceleration efficiency in the SNR RCW 86 from the Balmer emission. Since our calculation used recent measurements of the shock proper motion, the results depend on the assumed distance to Earth. For a distance of 2 kpc the measured width of the broad Balmer line is compatible with the absence of CR acceleration. For a distance of 2.5 kpc, which is a widely used value in current literature, a CR acceleration efficiency of 5-30% is obtained, depending upon the electron-ion equilibration and the ionization fraction upstream of the shock. By combining information on Balmer emission with the measured value of the downstream electron temperature, we constrain the CR acceleration efficiency to be ~20%. [ABSTRACT FROM AUTHOR]

We present the discovery of an unusual, tidally distorted extremely low mass white dwarf (WD) with nearly solar metallicity. Radial velocity measurements confirm that this is a compact binary with an orbital period of 2.6975 hr and a velocity semi-amplitude of K = 108.7 km s–1. Analysis of the hydrogen Balmer lines yields an effective temperature of Teff = 8380 K and a surface gravity of log g = 6.21 that in turn indicate a mass of M = 0.16 M☼ and a cooling age of 4.2 Gyr. In addition, a detailed analysis of the observed metal lines yields abundances of log (Mg/H) = –3.90, log (Ca/H) = –5.80, log (Ti/H) = –6.10, log (Cr/H) = –5.60, and log (Fe/H) = –4.50, similar to the sun. We see no evidence of a debris disk from which these metals would be accreted, though the possibility cannot entirely be ruled out. Other potential mechanisms to explain the presence of heavy elements are discussed. Finally, we expect this system to ultimately undergo unstable mass transfer and merge to form a ∼0.3-0.6 M☼ WD in a few Gyr. [ABSTRACT FROM AUTHOR]

Context. Balmer emission may be a powerful diagnostic tool for testing the paradigm of cosmic ray (CR) acceleration in young supernova remnant (SNR) shocks. The width of the broad Balmer line is a direct indicator of the downstream plasma temperature. In the case of efficient particle acceleration, an appreciable fraction of the total kinetic energy of the plasma is channeled into CRs, therefore the downstream temperature decreases and so does the broad Balmer line width. This width also depends on the level of thermal equilibration between ions and neutral hydrogen atoms in the downstream. Since generally only a few charge exchange (CE) reactions occur before ionization in young SNR shocks, equilibration between ions and neutrals is not reached, and a kinetic description of the neutrals is required to properly compute Balmer emission. Aims. We provide a method for calculating Balmer emission using a self-consistent description of the shock structure in the presence of neutrals and CRs, which also accounts for the non-Maxwellian distribution of neutrals. Methods. We use a recently developed semi-analytical approach, where neutral particles, ionized plasma, accelerated particles, and magnetic fields are all coupled together through the mass, momentum, and energy flux-conservation equations. The distribution of neutrals is obtained from the full Boltzmann equation in velocity space, coupled to Maxwellian ions through ionization and CE processes. The computation is also an improvement over previous work thanks to a better approximation of the atomic interaction rates. Results. We find that for shock speeds ≳2500 km s-1, the distribution of broad neutrals never approaches a Maxwellian and its moments differ from those of the ionized component. These differences lead to a smaller FWHM than predicted in previous calculations, where thermalization was assumed. Conclusions. The method presented here provides a realistic estimate of particle acceleration efficiency in Balmer-dominated shocks. [ABSTRACT FROM AUTHOR]

A Penning ion source with self-heated cathodes has been applied in a miniature cyclotron. Optimizing the formation of negative hydrogen ions in the ion source needs the knowledge of plasma parameters. Optical emission spectroscopy is introduced as a noninvasive and in situ diagnostic tool for line-of-sight averaged plasma parameters in this paper. The relative intensities of neutral atomic hydrogen emission spectral lines are used to evaluate the electron temperature of hydrogen plasma. The experimental results show that the relative intensities of Balmer lines (H\alpha, H\beta, and H\gamma) display significant dependence on gas flow rate, not sensible to arc current and magnetic field. The calculated electron temperature is in the range of 4000–7000 K in the experiments. The correlations of electron temperature with arc current, gas flow rate, and magnetic field are discussed, respectively. [ABSTRACT FROM AUTHOR]

Context. Observation of Balmer lines from the region around the forward shock of supernova remnants may provide precious information on the shock dynamics and on the efficiency of particle acceleration at the shock. Aims. We calculate the Balmer line emission and the shape of the broad Balmer line for parameter values suitable for SNR 0509-67.5, as a function of the cosmic ray acceleration efficiency and of the level of thermal equilibrium between electrons and protons behind the shock. This calculation aims to use the width of the broad Balmer line emission to infer the cosmic ray acceleration efficiency in this remnant. Methods. We use the recently developed nonlinear theory of diffusive shock acceleration in the presence of neutrals. The semianalytical approach that we developed includes a description of magnetic field amplification as due to resonant streaming instability, the dynamical reaction of both accelerated particles and turbulent magnetic field on the shock, and all channels of interaction between neutral atoms and background plasma that change the shock dynamics. Results. We achieve a quantitative assessment of the CR acceleration efficiency in SNR 0509-67.5 as a function of the shock velocity and different levels of electron-proton thermalization in the shock region. If the shock moves faster than ~4500 km s-1, one can conclude that particle acceleration must be taking place with an efficiency of several tens of percent. For lower shock velocity the evidence of particle acceleration becomes less clear because of the uncertainty in the electron-ion equilibrium downstream. We also discuss the role of future measurements of the narrow Balmer line. [ABSTRACT FROM AUTHOR]

Context. AA Tau has been monitored for more than 20 years since 1987 and exhibited a nearly constant brightness level of V = 12:5 mag. We report here that in 2011 it suddenly faded, becoming 2 mag fainter in the V-band, and has remained in this deep state since then. Aims. We investigate the origin of the sudden dimming of the AA Tau system. Methods. We report on new optical and near-IR photometry and spectroscopy obtained during the fading event. Results. The system appears to be much redder and fainter than it was in the bright state. Moreover, the 8.2 d photometric period continuously observed for more than 20 years is not detected during most of the deep state. The analysis of the system's brightness and colors suggests that the visual extinction on the line of sight has increased by about 3-4 mag in the deep state. At optical wavelengths, the system appears to be dominated by scattered light, probably originating from the upper surface layers of a highly inclined circumstellar disk. The profiles of the Balmer lines have significantly changed as well, with the disappearance of a central absorption component regularly observed in the bright state. We ascribe this change to the scattering of the system's spectrum by circumstellar dust. Remarkably, the mass accretion rate in the inner disk and onto the central star has not changed as the system faded. Conclusions. We conclude that the deepening of the AA Tau system is due to a sudden increase of circumstellar dust extinction on the line of sight without concomitant change in the accretion rate. We suggest that the enhanced obscuration may be produced by a nonaxisymmetric overdense region in the disk, located at a distance of 7.7 AU or more, that was recently brought into the line of sight by its Keplerian motion around the central star. [ABSTRACT FROM AUTHOR]

We use high-resolution imaging spectroscopy with the Swedish 1-m Solar Telescope (SST) to study the transient brightenings of the wings of the Balmer Hα line in emerging active regions that are called Ellerman bombs. Simultaneous sampling of Ca ii 8542 Å with the SST confirms that most Ellerman bombs also occur in the wings of this line, but with markedly different morphology. Simultaneous images from the Solar Dynamics Observatory (SDO) show that Ellerman bombs are also detectable in the photospheric 1700 Å continuum, again with differing morphology. They are also observable in 1600 Å SDO images, but with much contamination from Civ emission in transition-region features. Simultaneous SST spectropolarimetry in Fe i 6301 Å shows that Ellerman bombs occur at sites of strong-field magnetic flux cancellation between small bipolar strong-field patches that rapidly move together over the solar surface. Simultaneous SDO images in He ii 304 Å, Fe ix 171 Å, and Fe xiv 211 Å show no clear effect of the Ellerman bombs on the overlying transition region and corona. These results strengthen our earlier suggestion, based on Hα morphology alone, that the Ellerman bomb phenomenon is a purely photospheric reconnection phenomenon. [ABSTRACT FROM AUTHOR]

Aims. We attempt to determine if a dependency on spectral subtype or v sin i exists for stars undergoing phase-changes between B and Be states, as well as for those stars exhibiting variability in Ha emission. Methods. We analysed the changes in Ha line strength for a sample of 55 Be stars of varying spectral types and luminosity classes using five epochs of observations taken over a ten year period between 1998 and 2010. Results. We find i) that the typical timescale between which full phase transitions occur is most likely of the order of centuries, although no dependency on spectral subtype or v sin i could be determined due to the low frequency of phase-changing events observed in our sample; ii) that stars with earlier spectral types and larger values of v sin i show a greater degree of variability in Ha emission over the timescales probed in this study; and iii) a trend of increasing variability between the shortest and longest baselines for stars of later spectral types and with smaller values of v sin i. [ABSTRACT FROM AUTHOR]

We present the first X-ray study of NGC 6791, one of the oldest open clusters known (8 Gyr). Our Chandra observation is aimed at uncovering the population of close interacting binaries down to LX ≈ 1 × 1030 erg s-1 (0.3-7 keV). We detect 86 sources within 8' of the cluster center, including 59 inside the half-mass radius. We identify 20 sources with proper-motion cluster members, which are a mix of cataclysmic variables (CVs), active binaries (ABs), and binaries containing sub-subgiants. With follow-up optical spectroscopy, we confirm the nature of one CV. We discover one new, X-ray variable candidate CV with Balmer and He ii emission lines in its optical spectrum; this is the first X-ray-selected CV in an open cluster. The number of CVs per unit mass is consistent with the field, suggesting that the 3-4 CVs observed in NGC 6791 are primordial. We compare the X-ray properties of NGC 6791 with those of a few old open (NGC 6819, M 67) and globular clusters (47 Tuc, NGC 6397). It is puzzling that the number of ABs brighter than 1 × 1030 erg s-1 normalized by cluster mass is lower in NGC 6791 than in M 67 by a factor ~3-7. CVs, ABs, and sub-subgiants brighter than 1 × 1030 erg s-1 are under-represented per unit mass in the globular clusters compared to the oldest open clusters, and this accounts for the lower total X-ray luminosity per unit mass of the former. This indicates that the net effect of dynamical encounters may be the destruction of even some of the hardest (i.e., X-ray-emitting) binaries. [ABSTRACT FROM AUTHOR]

Recently, some hot DA-type white dwarfs have been proposed to plausibly be escaping members of the Hyades. We used hydrogen Balmer lines to measure the radial velocities of seven such stars and confirm that three, and perhaps two others, are/were indeed cluster members and one is not. The other candidate Hyad is strongly magnetic and its membership status remains uncertain. The photospheres of at least one quarter of field white dwarf stars are "polluted" by elements heavier than helium that have been accreted. These stars are orbited by extended planetary systems that contain both debris belts and major planets. We surveyed the seven classical single Hyades white dwarfs and the newly identified (escaping) Hyades white dwarfs and found calcium in the photosphere of LP 475-242 of type DBA (now DBAZ), thus implying the presence of an orbiting planetary system. The spectrum of white dwarf GD 31, which may be, but probably is not, an escaping member of the Hyades, displays calcium absorption lines; these originate either from the interstellar medium or, less likely, from a gaseous circumstellar disk. If GD 31 was once a Hyades member, then it would be the first identified white dwarf Hyad with a cooling age >340 Myr. [ABSTRACT FROM AUTHOR]

In this paper, we present the first formulation of the theory of nonlinear particle acceleration in collisionless shocks in the presence of neutral hydrogen in the acceleration region. The dynamical reaction of the accelerated particles, the magnetic field amplification, and the magnetic dynamical effects on the shock are also included. The main new aspect of this study, however, consists of accounting for charge exchange and the ionization of a neutral hydrogen, which profoundly change the structure of the shock, as discussed in our previous work. This important dynamical effect of neutrals is mainly associated with the so-called neutral return flux, namely the return of hot neutrals from the downstream region to upstream, where they deposit energy and momentum through charge exchange and ionization. We also present the self-consistent calculation of Balmer line emission from the shock region and discuss how to use measurements of the anomalous width of the different components of the Balmer line to infer cosmic ray acceleration efficiency in supernova remnants showing Balmer emission: the broad Balmer line, which is due to charge exchange of hydrogen atoms with hot ions downstream of the shock, is shown to become narrower as a result of the energy drainage into cosmic rays, while the narrow Balmer line, due to charge exchange in the cosmic-ray-induced precursor, is shown to become broader. In addition to these two well-known components, the neutral return flux leads to the formation of a third component with an intermediate width: this too contains information on ongoing processes at the shock. [ABSTRACT FROM AUTHOR]

Context. Early B-type stars are ideal indicators for present-day cosmic abundances since they preserve their pristine abundances and typically do not migrate far beyond their birth environments over their short lifetimes, in contrast to older stars like the Sun. They are also unaffected by depletion onto dust grains, unlike the cold/warm interstellar medium (ISM) or Hii regions. Aims. A carefully selected sample of early B-type stars in OB associations and the field within the solar neighbourhood is studied comprehensively. Quantitative spectroscopy is used to characterise their atmospheric properties in a self-consistent way. Present-day abundances for the astrophysically most interesting chemical elements are derived in order to investigate whether a present-day cosmic abundance standard can be established. Methods. High-resolution and high-S/N FOCES, FEROS and ELODIE spectra of well-studied sharp-lined early B-type stars are analysed in non-LTE. Line-profile fits based on extensive model grids and an iterative analysis methodology are used to constrain stellar parameters and elemental abundances at high accuracy and precision. Atmospheric parameters are derived from the simultaneous establishment of independent indicators, from multiple ionization equilibria and the Stark-broadened hydrogen Balmer lines, and they are confirmed by reproduction of the stars' global spectral energy distributions. Results. Effective temperatures are constrained to 1-2% and surface gravities to less than 15% uncertainty, along with accurate rotational, micro- and macroturbulence velocities. Good agreement of the resulting spectroscopic parallaxes with those from the new reduction of the Hipparcos catalogue is obtained. Absolute values for abundances of He, C, N, O, Ne, Mg, Si and Fe are determined to better than 25% uncertainty. The synthetic spectra match the observations reliably over almost the entire visual spectral range. Three sample stars, γ Ori, o Per and ϴ1 OriD, are identified as double-lined, indicating the presence of an early/mid B-type companion. Conclusions. A present-day cosmic abundance standard is established from a sample of 29 early B-type stars, indicating abundance fluctuations of less than 10% around the mean. Our results (i) resolve the long-standing discrepancy between a chemical homogeneous gas-phase ISM and a chemically inhomogeneous young stellar component out to several hundred parsec from the Sun, (ii) facilitate the amount of heavy elements locked up in the interstellar dust to be constrained precisely - the results imply that carbonaceous dust is largely destroyed inside the Orion Hii region, unlike the silicates, and that graphite is only a minority species in interstellar dust -, (iii) show that the mixing of CNO-burning products in the course of massive star evolution follows tightly the predicted nuclear path, (iv) provide reliable present-day reference points for anchoring Galactic chemical evolution models to observation, and (v) imply that the Sun has migrated outwards from the inner Galactic disk over its lifetime from a birthplace at a distance around 5-6 kpc from the Galactic Centre; a cancellation of the effects of Galactic chemical evolution and abundance gradients leads to the similarity of solar and present-day cosmic abundances in the solar neighbourhood, with a telltaling signature of the Sun's origin left in the C/O ratio. [ABSTRACT FROM AUTHOR]

We present the discovery of strong Balmer line absorption in Hα to Hγ in two luminous low-ionization broad absorption line quasars at , with black hole masses around from near-IR spectroscopy. There are only two previously known quasars at showing Balmer line absorption. SDSS J1019+0225 shows blueshifted absorption by ∼1400 km s−1 with an Hα rest-frame equivalent width of 13 Å. In SDSS J0859+4239, we find redshifted absorption by ∼500 km s−1 with an Hα rest-frame equivalent width of 7 Å. The redshifted absorption could indicate an inflow of high-density gas onto the black hole, though we cannot rule out alternative interpretations. The Balmer line absorption in both objects appears to be saturated, indicating partial coverage of the background source by the absorber. We estimate the covering fractions and optical depth of the absorber and derive neutral hydrogen column densities, NH i ∼ 1.3 × 1018 cm−2 for SDSS J1019+0225 and NH i ∼ 9 × 1017 cm−2 for SDSS J0859+4239. In addition, the optical spectra reveal also absorption troughs in He i* and in both objects. [ABSTRACT FROM AUTHOR]

Spectroscopy on the globular cluster (GC) system of NGC 5128 revealed bimodality in absorption-line index distributions of its old GCs. GC division is a widely observed and studied phenomenon whose interpretation has depicted host galaxy formation and evolution such that it harbors two distinct metallicity groups. Such a conventional view of GC bimodality has mainly been based on photometry. The recent GC photometric data, however, presented an alternative perspective in which the nonlinear metallicity-to-color transformation is responsible for color bimodality of GC systems. Here we apply the same line of analysis to the spectral indices and examine the absorption-line index versus metallicity relations for the NGC 5128 GC system. NGC 5128 GCs display nonlinearity in the metallicity-index planes, most prominently for the Balmer lines and by a non-negligible degree for the metallicity-sensitive magnesium line. We demonstrate that the observed spectroscopic division of NGC 5128 GCs can be caused by the nonlinear nature of the metallicity-to-index conversions and thus one does not need to resort to two separate GC subgroups. Our analysis incorporating this nonlinearity provides a new perspective on the structure of NGC 5128's GC system, and a further piece to the global picture of the formation of GC systems and their host galaxies. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) are extremely powerful cosmic objects, driven by accretion of hot gas upon super-massive black holes. The zoo of AGN classes is divided into two major groups, with Type-1 AGNs displaying broad Balmer emission lines and Type-2 narrow ones. For a long time it was believed that a Type-2 AGN is a Type-1 AGN viewed through a dusty kiloparsec-sized torus, but an emerging body of observations suggests more than just the viewing angle matters. Here we report significant differences in supernova (SN) counts and classes in the first study to date of SNe near Type-1 and Type-2 AGN host galaxies, using data from the intermediate Palomar Transient Factory, the Sloan Digital Sky Survey Data Release 7, and Galaxy Zoo. We detect many more SNe in Type-2 AGN hosts (size of effect ∼5.1σ) compared to Type-1 hosts, which shows that the two classes of AGN are located inside host galaxies with different properties. In addition, Type-1 and Type-2 AGNs that are dominated by star formation according to Wide-field Infrared Survey Explorer colors and are matched in 22 μm absolute magnitude differ by a factor of ten in L[O iii] λ5007 luminosity, suggesting that when residing in similar types of host galaxies Type-1 AGNs are much more luminous. Our results demonstrate two more factors that play an important role in completing the current picture: the age of stellar populations and the AGN luminosity. This has immediate consequences for understanding the many AGN classes and galaxy evolution. [ABSTRACT FROM AUTHOR]

Continuum (“white-light,” WL) emission dominates the energetics of flares. Filter-based observations, such as the IRIS SJI 2832 filter, show WL-like brightenings during flares, but it is unclear whether the emission arises from real continuum emission or enhanced spectral lines, possibly turning into emission. The difficulty in filter-based observations, contrary to spectral observations, is to determine which processes contribute to the observed brightening during flares. Here we determine the contribution of the Balmer continuum and the spectral line emission to IRIS’ SJI 2832 emission by analyzing the appropriate passband in simultaneous IRIS NUV spectra. We find that spectral line emission can contribute up to 100% to the observed slitjaw images (SJI) emission, that the relative contributions usually temporally vary, and that the highest SJI enhancements that are observed are most likely because of the Balmer continuum. We conclude that care should be taken when calling SJI 2832 a continuum filter during flares, because the influence of the lines on the emission can be significant. [ABSTRACT FROM AUTHOR]

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate diagnostic of the degree of ionization and compression resulting from flare heating in the chromosphere. To resolve this issue, we have incorporated the unified theory of electric pressure broadening of the hydrogen lines into the non-LTE radiative-transfer code RH. This broadening prescription produces a much more realistic spectrum of the quiescent, A0 star Vega compared to the analytic approximations used as a damping parameter in the Voigt profiles. We test recent radiative-hydrodynamic (RHD) simulations of the atmospheric response to high nonthermal electron beam fluxes with the new broadening prescription and find that the Balmer lines are overbroadened at the densest times in the simulations. Adding many simultaneously heated and cooling model loops as a “multithread” model improves the agreement with the observations. We revisit the three-component phenomenological flare model of the YZ CMi Megaflare using recent and new RHD models. The evolution of the broadening, line flux ratios, and continuum flux ratios are well-reproduced by a multithread model with high-flux nonthermal electron beam heating, an extended decay phase model, and a “hot spot” atmosphere heated by an ultrarelativistic electron beam with reasonable filling factors: ∼0.1%, 1%, and 0.1% of the visible stellar hemisphere, respectively. The new modeling motivates future work to understand the origin of the extended gradual phase emission. [ABSTRACT FROM AUTHOR]

Broad (∼10,000 km s−1), double-peaked emission-line profiles of Balmer lines emitted by active galactic nuclei (AGN) are thought to originate in the outer parts of an accretion disk surrounding a nuclear supermassive black hole (SMBH), at ∼1000 gravitational radii, and are most frequently observed in the nuclear spectra of low-luminosity AGN (LLAGN) and radio galaxies. In the present paper we argue that broad double-peaked profiles are present also in the spectra of other type 1 AGN, such as Seyfert 1 galaxies, suggesting that the inner part of the broad-line region (BLR) is also the outer part of the accretion disk. We use the Palomar spectral survey of nearby galaxies to show that the only difference between Seyfert 1 BLR line profiles and “bona fide” double-peakers is that, in most cases, besides a disk component, we need an additional Gaussian component attributed to nondisk clouds. The recognition that the inner and most variable part of the BLR has a disk geometry suggests that the factor f in the expression to obtain the SMBH mass in type 1 AGN, , is for the disk-dominated sources. Our median i = 27° implies f = 4.5, very close to the most recent value of f = 4.3 ± 1.05, obtained from independent studies. We derive a relation between f and the FWHM of the broad profile that may help to reduce the uncertainties in the SMBH mass determinations of AGN. [ABSTRACT FROM AUTHOR]

We present a new metric that uses the spectral curvature (SC) above 10 keV to identify Compton-thick active galactic nuclei (AGNs) in low-quality Swift/Burst Alert Telescope (BAT) X-ray data. Using NuSTAR, we observe nine high SC-selected AGNs. We find that high-sensitivity spectra show that the majority are Compton-thick (78% or 7/9) and the remaining two are nearly Compton-thick (NH ≃ (5–8) × 1023 cm−2 ). We find that the SC BAT and SC NuSTAR measurements are consistent, suggesting that this technique can be applied to future telescopes. We tested the SC method on well-known Compton-thick AGNs and found that it is much more effective than broadband ratios (e.g., 100% using SC versus 20% using 8–24 keV/3–8 keV). Our results suggest that using the >10 keV emission may be the only way to identify this population since only two sources show Compton-thick levels of excess in the Balmer decrement corrected [O iii] to observed X-ray emission ratio () and WISE colors do not identify most of them as AGNs. Based on this small sample, we find that a higher fraction of these AGNs are in the final merger stage (<10 kpc) than typical BAT AGNs. Additionally, these nine obscured AGNs have, on average, ≈4× higher accretion rates than other BAT-detected AGNs ( compared to ). The robustness of SC at identifying Compton-thick AGNs implies that a higher fraction of nearby AGNs may be Compton-thick (≈22%) and the sum of black hole growth in Compton-thick AGNs (Eddington ratio times population percentage) is nearly as large as mildly obscured and unobscured AGNs. [ABSTRACT FROM AUTHOR]

We report on the discovery of broad Balmer absorption lines variability in the QSO SDSS J125942.80+121312.6, based on the optical and near-infrared spectra taken from the SDSS-I, SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), and TripleSpec observations over a timescale of 5.8 years in the QSO's rest-frame. The blueshifted absorption profile of Hβ shows a variation of more than 5σ at a high velocity portion () of the trough. We perform a detailed analysis for the physical conditions of the absorber using Balmer lines as well as metastable He i and optical Fe ii absorptions (λ4233 from b4P5/2 level and λ5169 from a6S5/2) at the same velocity. These Fe ii lines are identified in the QSO spectra for the first time. According to the photoionization simulations, we estimate a gas density of and a column density of for the BOSS data, but the model fails to predict the variations of ionic column densities between the SDSS and BOSS observations if changes in ionizing flux are assumed. We thus propose transverse motion of the absorbing gas being the cause of the observed broad Balmer absorption line variability. In fact, we find that the changes in covering factors of the absorber can well-reproduce all of the observed variations. The absorber is estimated ∼0.94 pc away from the central engine, which is where the outflow likely experiences deceleration due to the collision with the surrounding medium. This scheme is consistent with the argument that LoBAL QSOs may represent the transition from obscured star-forming galaxies to classic QSOs. [ABSTRACT FROM AUTHOR]

We present Keck/Echellette Spectrograph and Imager long-slit spectroscopy of SBS 1421+511, a system consisting of a quasar at z = 0.276 and an extended source 3″ north of the quasar. The quasar shows a blue-skewed profile of Balmer broad emission lines, which can be well modeled as emissions from a circular disk with a blueshift velocity of ∼1400 km s−1. The blueshift is better interpreted as resulting from a recoiling active black hole than from a super-massive black hole binary, since the line profile almost kept steady for over one decade in the quasar rest frame. Alternative interpretations are possible as well, such as emissions from a bipolar outflow or a circular disk with spiral emissivity perturbations. The extended source shows Seyfert-like narrow-line ratios and a [O iii] luminosity of , with almost the same redshift as the quasar and a projected distance of 12.5 kpc at the redshift. SBS 1421+511 is thus likely to be an interacting galaxy pair with a dual active galactic nucleus. Alternatively, the quasar companion only appears to be active but not necessarily so: the gas before/in/behind the companion galaxy is illuminated by the quasar as an extended emission-line region is detected at a similar distance in the opposite direction southern to the quasar, which may be generated either by tidal interactions between the galaxy pair or large-scale outflows from the quasar. [ABSTRACT FROM AUTHOR]

Recently, a suspicion arose that the free electrons in planetary nebulae (PNs) and H ii regions might have nonthermal energy distributions. In this scenario, a κ index is introduced to characterize the electron energy distributions, with smaller κ values indicating larger deviations from Maxwell–Boltzmann distributions. Assuming that this is the case, we determine the κ values for a sample of PNs and H ii regions by comparing the intensities of [O iii] collisionally excited lines and the hydrogen Balmer jump. We find the average κ indices of PNs and H ii regions to be 27 and 32, respectively. Correlations between the resultant κ values and various physical properties of the nebulae are examined to explore the potential origin of nonthermal electrons in photoionized gaseous nebulae. However, no positive result is obtained. Thus, the current analysis does not lend support to the idea that κ-distributed electrons are present in PNs and H ii regions. [ABSTRACT FROM AUTHOR]

We examine the redshift evolution of standard strong emission-line diagnostics for Hβ-selected star-forming galaxies using the local SDSS sample and a new sample obtained from Hubble Space Telescope WFC3 grism and Keck DEIMOS and MOSFIRE data. We use the SDSS galaxies to show that there is a systematic dependence of the strong emission-line properties on Balmer-line luminosity, which we interpret as showing that both the N/O abundance and the ionization parameter increase with increasing line luminosity. Allowing for the luminosity dependence tightens the diagnostic diagrams and the metallicity calibrations. The combined SDSS and high-redshift samples show that there is no redshift evolution in the line properties once the luminosity correction is applied, i.e., all galaxies with a given ) have similar strong emission-line distributions at all the observed redshifts. We argue that the best metal diagnostic for the high-redshift galaxies may be a luminosity-adjusted version of the [N ii]6584/Hα metallicity relation. [ABSTRACT FROM AUTHOR]

One of the proposed explanations for the broad, double-peaked Balmer emission lines observed in the spectra of some active galactic nuclei (AGNs) is that they are associated with sub-parsec supermassive black hole (SMBH) binaries. Here, we test the binary broad-line region hypothesis through several decades of monitoring of the velocity structure of double-peaked Hα emission lines in 13 low-redshift, mostly radio-loud AGNs. This is a much larger set of objects compared to an earlier test by Eracleous et al. and we use much longer time series for the three objects studied in that paper. Although systematic changes in radial velocity can be traced in many of their lines, they are demonstrably not like those of a spectroscopic binary in a circular orbit. Any spectroscopic binary period must therefore be much longer than the span of the monitoring (assuming a circular orbit), which in turn would require black hole masses that exceed by 1–2 orders of magnitude the values obtained for these objects using techniques such as reverberation mapping and stellar velocity dispersion. Moreover, the response of the double-peaked Balmer line profiles to fluctuations of the ionizing continuum and the shape of the Lyα profiles are incompatible with an SMBH binary. The binary broad-line region hypothesis is therefore disfavored. Other processes evidently shape these line profiles and cause the long-term velocity variations of the double peaks. [ABSTRACT FROM AUTHOR]

We present results on the star formation rate (SFR) versus stellar mass (M*) relation (i.e., the “main sequence”) among star-forming galaxies at 1.37 ≤ z ≤ 2.61 using the MOSFIRE Deep Evolution Field (MOSDEF) survey. Based on a sample of 261 galaxies with Hα and Hβ spectroscopy, we have estimated robust dust-corrected instantaneous SFRs over a large range in M* (∼109.5–1011.5M⊙). We find a correlation between log(SFR(Hα)) and log(M*) with a slope of 0.65 ± 0.08 (0.58 ± 0.10) at 1.4 < z < 2.6 (2.1 < z < 2.6). We find that different assumptions for the dust correction, such as using the color excess of the stellar continuum to correct the nebular lines, sample selection biases against red star-forming galaxies, and not accounting for Balmer absorption, can yield steeper slopes of the log(SFR)–log(M*) relation. Our sample is immune from these biases as it is rest-frame optically selected, Hα and Hβ are corrected for Balmer absorption, and the Hα luminosity is dust corrected using the nebular color excess computed from the Balmer decrement. The scatter of the log(SFR(Hα))–log(M*) relation, after accounting for the measurement uncertainties, is 0.31 dex at 2.1 < z < 2.6, which is 0.05 dex larger than the scatter in log(SFR(UV))–log(M*). Based on comparisons to a simulated SFR–M* relation with some intrinsic scatter, we argue that in the absence of direct measurements of galaxy-to-galaxy variations in the attenuation/extinction curves and the initial mass function, one cannot use the difference in the scatter of the SFR(Hα)– and SFR(UV)–M* relations to constrain the stochasticity of star formation in high-redshift galaxies. [ABSTRACT FROM AUTHOR]

We present the discovery of Balmer line absorption from Hα to Hγ in an iron low-ionization broad absorption line (FeLoBAL) quasar SDSS J152350.42+391405.2 (hereafter SDSS J1523+3914), by the quasi-simultaneous optical and near-infrared spectroscopy. The Balmer line absorption is at and blueshifted by v = 10,353 km s−1 with respect to the Balmer emission lines. All Balmer BALs have a uniform absorption profile with the widths of 12,000 km s−1. We also found the absorption trough in He i* λ10830 with the same velocity and width in the H-band TripleSpec spectrum of SDSS J1523+3914. This object is only the 10th active galactic nucleus known to exhibit nonstellar Balmer absorption, as well as the case with the highest velocity and broadest Balmer absorption lines that have ever been found. A CLOUDY analysis shows that the absorbers require a gas density of and an ionization parameter of They are located at a distance of ∼0.2 pc from the central ionizing source, which is slightly farther than that of broad emission line regions. Furthermore, SDSS J1523+3914 is one of the brightest Balmer BAL quasars ever reported, with unique iron absorption variations, making it the most promising candidate for follow-up high-resolution spectroscopy, multiband observations, and long-term monitoring. [ABSTRACT FROM AUTHOR]