Absolute Bolometric Magnitude Research Articles

Supernova 2020wnt: An Atypical Superluminous Supernova with a Hidden Central Engine

We present observations of a peculiar hydrogen- and helium-poor stripped-envelope (SE) supernova (SN) 2020wnt, primarily in the optical and near-infrared (near-IR). Its peak absolute bolometric magnitude of −20.9 mag (L bol, peak = (6.8 ± 0.3) × 1043 erg s−1) and a rise time of 69 days are reminiscent of hydrogen-poor superluminous SNe (SLSNe I), luminous transients potentially powered by spinning-down magnetars. Before the main peak, there is a brief peak lasting <10 days post explosion, likely caused by interaction with circumstellar medium (CSM) ejected ∼years before the SN explosion. The optical spectra near peak lack a hot continuum and O ii absorptions, which are signs of heating from a central engine; they quantitatively resemble those of radioactivity-powered hydrogen/helium-poor Type Ic SESNe. At ∼1 yr after peak, nebular spectra reveal a blue pseudo-continuum and narrow O i recombination lines associated with magnetar heating. Radio observations rule out strong CSM interactions as the dominant energy source at +266 days post peak. Near-IR observations at +200–300 days reveal carbon monoxide and dust formation, which causes a dramatic optical light-curve dip. Pair-instability explosion models predict slow light curve and spectral features incompatible with observations. SN 2020wnt is best explained as a magnetar-powered core-collapse explosion of a 28 M ⊙ pre-SN star. The explosion kinetic energy is significantly larger than the magnetar energy at peak, effectively concealing the magnetar-heated inner ejecta until well after peak. SN 2020wnt falls into a continuum between normal SNe Ic and SLSNe I, and demonstrates that optical spectra at peak alone cannot rule out the presence of a central engine.

S-type Stars Discovered in Medium-resolution Spectra of LAMOST DR9

In this paper, we report on 606 S-type stars identified from Data Release 9 of the LAMOST medium-resolution spectroscopic (MRS) survey; 539 of them are reported for the first time. The discovery of these stars is a three-step process, i.e., selecting with ZrO-band indices greater than 0.25, excluding non-S-type stars with the iterative Support Vector Machine method, and finally retaining stars with absolute bolometric magnitude larger than −7.1. The 606 stars are consistent with the distribution of known S-type stars in the color–magnitude diagram. We estimated the C/Os using the [C/Fe] and [O/Fe] provided by APOGEE and the MARCS model for S-type stars, respectively, and the results of the two methods show that the C/Os of all stars are larger than 0.5. Both the locations on the color–magnitude diagram and C/Os further verify the nature of our S-type sample. Investigating the effect of TiO and atmospheric parameters on ZrO with the sample, we found that log g has a more significant impact on ZrO than T eff and [Fe/H], and both TiO and log g may negatively correlate with ZrO. According to the criterion of Tian et al., a total of 238 binary candidates were found by the zero-point-calibrated radial velocities from the officially released catalog of LAMOST MRS and the catalog of Zhang et al. A catalog of these 606 S-type stars is available from the following link: doi.org/10.12149/101097.

Characterizing the Evolved Stellar Population in the Galactic Foreground. I. Bolometric Magnitudes, Spatial Distribution and Period–Luminosity Relations

Abstract Radio campaigns using maser stellar beacons have provided crucial information to characterize Galactic stellar populations. Currently, the Bulge Asymmetries and Dynamical Evolution (BAaDE) project is surveying infrared (IR) color-selected targets for SiO masers. This provides a sample of evolved stars that can be used to study the inner, optically obscured Galaxy using line-of-sight velocities and possibly very long baseline interferometry proper motions. In order to use the BAaDE sample for kinematic studies, the stellar population should be characterized. In this study, the BAaDE targets have been cross-matched with IR (2MASS) and optical (Gaia) samples. By exploring the synergies of this cross-match together with Gaia parallaxes and extinction maps, the local (d &lt; 2 kpc) asymptotic giant branch (AGB) stars can be characterized. We have defined a BAaDE–Gaia sample of 20,111 sources resulting from cross-matching BAaDE targets with IR and optical surveys. From this sample, a local sample of 1812 evolved stars with accurate parallax measurements, confirmed evolved stellar evolution stage, and within 2 kpc distance around the Sun was selected, for which absolute (bolometric) magnitudes are estimated. The evolved stellar population with Gaia counterparts that are variable seems to be predominantly associated with AGB stars with moderate luminosity ( ) and periods between 250 and 1250 days.

A Simple Unified Spectroscopic Indicator of Stellar Luminosity: The Extended Flux-weighted Gravity–Luminosity Relationship

Abstract We show that for a wide range of stellar masses, from 0.3 to 20 M ⊙, and for evolutionary phases from the main sequence to the beginning of the red giant stage, the stellar flux-weighted gravity, g F ≡ g/ , is tightly correlated with absolute bolometric magnitude . Such a correlation is predicted by stellar evolution theory. We confirm this relation observationally, using a sample of 445 stars with precise stellar parameters. It holds over 17 stellar magnitudes from = 9.0 to −8.0 mag with a scatter of 0.17 mag above = −3.0 and 0.29 mag below this value. We then test the relation with 2.2 million stars with 6.5 mag ≥ ≥ 0.5 mag, where “mass-produced” but robust , and from LAMOST DR5 and Gaia DR2 are available. We find that the same relation holds with a scatter of ∼0.2 mag for single stars offering a simple spectroscopic distance estimate good to ∼10%.

On the long-cycle variability of the Algol OGLE-LMC-DPV-065 and its stellar, orbital, and disc parameters

OGLE-LMC-DPV-065 is an interacting binary whose double-hump long photometric cycle remains hitherto unexplained. We analyze photometric time series available in archive datasets spanning 124 years and present the analysis of new high-resolution spectra. A refined orbital period is found of 10\fd0316267 $\pm$ 0\fd0000056 without any evidence of variability. In spite of this constancy, small but significant changes in timings of the secondary eclipse are detected. We show that the long period continuously decreases from 350 to 218 days during 13 years, then remains almost constant for about 10 years. Our study of radial velocities indicates a circular orbit for the binary and yields a mass ratio of 0.203 $\pm$ 0.001. From the analysis of the orbital light curve we find that the system contains 13.8 and 2.81 \msun\ stars of radii 8.8 and 12.6 \rsun\ and absolute bolometric magnitudes -6.4 and -3.0, respectively. The orbit semi-major axis is 49.9 \rsun\ and the stellar temperatures are 25460 K and 9825 K. We find evidence for an optically and geometrically thick disk around the hotter star. According to our model, the disk has a radius of 25 \rsun, central and outer vertical thickness of 1.6 \rsun\ and 3.5 \rsun, and temperature of 9380 K at its outer edge. Two shock regions located at roughly opposite parts of the outer disk rim can explain the light curves asymmetries. The system is a member of the double periodic variables and its relatively high-mass and long photometric cycle make it similar in some aspects to $\beta$ Lyrae.

Impact of binary interaction on the evolution of blue supergiants

A large fraction of massive stars evolve in interacting binary systems, which dramatically modifies the outcome of stellar evolution. We investigated the properties of blue supergiants in binary systems and whether they are suitable for extragalactic distance determinations using the flux-weighted gravity luminosity relationship (FGLR). This is a relationship between the absolute bolometric magnitude Mbol and the spectroscopically determined flux-weighted gravity gF = g/T4eff, where g is the surface gravity and Teff is the effective temperature. We computed a grid of binary stellar evolution models with MESA and use the v2.1 BPASS models to examine whether they are compatible with the relatively small scatter shown by the observed relationship. Our models have initial primary masses of 9–30 M⊙, initial orbital periods of 10–2511 days, mass ratio q = 0.9, and metallicity Z = 0.02. We find that the majority of primary stars that produce blue supergiant stages are consistent with the observed FGLR, with a small offset towards brighter bolometric magnitudes. In between 1%–24% of cases, binary evolution may produce blue supergiants after a mass transfer episode, that lie below the observed FGLR. A very small number of such stars have been found in extragalactic FGLR studies, suggesting that they may have evolved through binary interaction. Some models with shorter periods could resemble blue hypergiants and luminous blue variables. We used CMFGEN radiative transfer models to investigate the effects of unresolved secondaries on diagnostics for Teff and g, and the biases on the determination of interstellar reddening and Mbol. We find that the effects are small and within the observed scatter, but could lead to a small overestimate of the luminosity, of Teff and of g for extreme cases. We conclude that the observed FGLR can, in principle, be well reproduced by close binary evolution models. We outline directions for future work, including rotation and binary population synthesis techniques.

LMC Blue Supergiant Stars and the Calibration of the Flux-weighted Gravity–Luminosity Relationship

Abstract High-quality spectra of 90 blue supergiant stars in the Large Magellanic Cloud are analyzed with respect to effective temperature, gravity, metallicity, reddening, extinction, and extinction law. An average metallicity, based on Fe and Mg abundances, relative to the Sun of [Z] = −0.35 ± 0.09 dex is obtained. The reddening distribution peaks at = 0.08 mag, but significantly larger values are also encountered. A wide distribution of the ratio of extinction to reddening is found ranging from = 2 to 6. The results are used to investigate the blue supergiant relationship between flux-weighted gravity, g f ≡ g/ , and absolute bolometric magnitude M bol. The existence of a tight relationship, the Flux-weighted Gravity–Luminosity Relationship (FGLR), is confirmed. However, in contrast to previous work, the observations reveal that the FGLR is divided into two parts with a different slope. For flux-weighted gravities larger than 1.30 dex, the slope is similar to that found in previous work, but the relationship becomes significantly steeper for smaller values of the flux-weighted gravity. A new calibration of the FGLR for extragalactic distance determinations is provided.

Confronting the Gaia and NLTE spectroscopic parallaxes for the FGK stars

AbstractThe understanding of the chemical evolution of the Galaxy relies on the stellar chemical composition. Accurate atmospheric parameters is a prerequisite of determination of accurate chemical abundances. For late type stars with known distance, surface gravity (log g) can be calculated from well-known relation between stellar mass, Teff, and absolute bolometric magnitude. This method weakly depends on model atmospheres, and provides reliable log g. However, accurate distances are available for limited number of stars. Another way to determine log g for cool stars is based on ionisation equilibrium, i.e. consistent abundances from lines of neutral and ionised species. In this study we determine atmospheric parameters moving step-by-step from well-studied nearby dwarfs to ultra-metal poor (UMP) giants. In each sample, we select stars with the most reliable Teff based on photometry and the distance-based log g, and compare with spectroscopic gravity calculated taking into account deviations from local thermodinamic equilibrium (LTE). After that, we apply spectroscopic method of log g determination to other stars of the sample with unknown distances.

Fundamental parameters of B type stars

AbstractFundamental parameters of 26 well-studied sharp-lined single early B-type stars in OB associations and in the field within a distance of ≤400 pc from the Sun are compared to high-precision data from detached eclipsing binaries (DEBs). Fundamental parameters are derived from accurate and precise atmospheric parameters determined earlier by us from non-LTE analyses of high-quality spectra, utilising the new Geneva stellar evolution models in the mass-range ~6 to 18 M⊙ at metallicity Z = 0.014. Evolutionary masses, radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass-radius and mass-luminosity relationships to be recovered for single core hydrogen-burning objects with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically ~0.15-0.20 mag uncertainty. Metallicities are constrained to better than 15-20% uncertainty and tight constraints on evolutionary ages of the stars are provided. The spectroscopic distances and ages of individual sample stars agree with independently derived values for the host OB associations. The accuracy and precision achieved in the determination of fundamental stellar parameters from the quantitative spectroscopy of single early B-type stars comes close (within a factor 2-4) to data derived from DEBs.

Fundamental properties of nearby single early B-type stars

Fundamental parameters of a sample of 26 apparently slowly-rotating single early B-type stars in the solar neighbourhood are presented and compared to high-precision data from detached eclipsing binaries (DEBs). The data are used to discuss the evolutionary status of the stars in context of the most recent Geneva grid of models. Evolutionary masses plus radii and luminosities are determined to better than typically 5%, 10%, and 20% uncertainty, respectively, facilitating the mass-radius and mass-luminosity relationships to be recovered with a similar precision as derived from DEBs. Good agreement between evolutionary and spectroscopic masses is found. Absolute visual and bolometric magnitudes are derived to typically 0.15-0.20mag uncertainty. Metallicities are constrained to better than 15-20% uncertainty and tight constraints on evolutionary ages of the stars are provided. Signatures of mixing with CN-cycled material are found in 1/3 of the sample stars. Typically, these are consistent with the amount predicted by the new Geneva models with rotation. A few objects are possibly the product of binary evolution. In particular, the unusual characteristics of tau Sco point to a blue straggler nature, due to a binary merger. The accuracy and precision achieved in the determination of fundamental stellar parameters from the quantitative spectroscopy of single early B-type stars comes close (within a factor 2-4) to data derived from DEBs. However, significant systematic differences with data from the astrophysical reference literature are found. Masses are about 10-20% and radii about 25% lower then the recommended values for luminosity class V, resulting in the stars being systematically fainter than assumed usually, by about 0.5mag in absolute visual and bolometric magnitude. (abstract abridged)

SYSTEMATICS OF DYNAMICAL MASS EJECTION, NUCLEOSYNTHESIS, AND RADIOACTIVELY POWERED ELECTROMAGNETIC SIGNALS FROM NEUTRON-STAR MERGERS

We investigate systematically the dynamical mass ejection, r-process nucleosynthesis, and properties of electromagnetic counterparts of neutron-star (NS) mergers in dependence on the uncertain properties of the nuclear equation of state (EoS) by employing 40 representative, microphysical high-density EoSs in relativistic, hydrodynamical simulations. The crucial parameter determining the ejecta mass is the radius R_1.35 of a 1.35 M_sun NS. NSs with smaller R_1.35 ("soft" EoS) eject systematically higher masses. These range from ~10^-3 M_sun to ~10^-2 M_sun for 1.35-1.35 M_sun binaries and from ~5*10^-3 M_sun to ~2*10^-2 M_sun for 1.2-1.5 M_sun systems (with kinetic energies between ~5*10^49 erg and 10^51 erg). Correspondingly, the bolometric peak luminosities of the optical transients of symmetric (asymmetric) mergers vary between 3*10^41 erg/s and 14*10^41 erg/s (9*10^41 erg/s and 14.5*10^41 erg/s) on timescales between ~2 h and ~12 h. If these signals with absolute bolometric magnitudes from -15.0 to -16.7 are measured, the tight correlation of their properties with those of the merging NSs might provide valuable constraints on the high-density EoS. The r-process nucleosynthesis exhibits a remarkable robustness independent of the EoS, producing a nearly solar abundance pattern above mass number 130. By the r-process content of the Galaxy and the average production per event the Galactic merger rate is limited to 4*10^-5/yr (4*10^-4/yr) for a soft (stiff) NS EoS, if NS mergers are the main source of heavy r-nuclei. The production ratio of radioactive 232Th to 238U attains a stable value of 1.64-1.67, which does not exclude NS mergers as potential sources of heavy r-material in the most metal-poor stars.

The hypergiant HR 8752 evolving through the yellow evolutionary void

Context. We study the time history of the yellow hypergiant HR 8752 based on high-resolution spectra (1973–2005), the observed MK spectral classification data, B − V -a ndV-observations (1918–1996) and yet earlier V-observations (1840–1918). Aims. Our local thermal equilibrium analysis of the spectra yields accurate values of the effective temperature (Teff), the acceleration of gravity (g), and the turbulent velocity (vt) for 26 spectra. The standard deviations average are 82 K for Teff ,0 .23 for logg, and 1.1 km s −1 for vt. Methods. A comparison of B−V observations, MK spectral types, and Teff-data yields E(B−V), “intrinsic” B−V,Teff, absorption AV, and the bolometric correction BC. With the additional information from simultaneous values of B −V,V, and an estimated value of R, the ratio of specific absorption to the interstellar absorption parameter E(B − V), the “unreddened” bolometric magnitude mbol,0 can be determined. With Hipparcos distance measurements of HR 8752, the absolute bolometric magnitude Mbol,0 can be determined. Results. Over the period of our study, the value of Teff gradually increased during a number of downward excursions that were observable over the period of sufficient time coverage. These observations, together with those of the effective acceleration g and the turbulent velocity vt, suggest that the star underwent a number of successive gas ejections. During each ejection, a pseudo photosphere was produced of increasingly smaller g and higher vt values. After the dispersion into space of the ejected shells and after the restructuring of the star’s atmosphere, a hotter and more compact photosphere became visible. From the B −V and V observations, the basic

SDSS DR4: Progress on the hot white dwarf luminosity function

A large collection of white dwarf (WD) spectra from Sloan Digital Sky Survey (SDSS) data release 4 (DR4) WD catalog data allowed us to obtain a luminosity function (LF) for the hottest WDs. The LF was calculated basing on spectra of the WDs from a special class of SDSS objects called hot standards (HS), for which the WD sample completeness can be estimated. WD distances were determined from the observed and absolute SDSS g filter magnitudes derived from WD stellar atmosphere model fits to the SDSS spectra. The result LF covers -0.5 up to 7 absolute bolometric magnitude range. It shows a slight disagreement at the cold end comparing to the literature LFs but it can be due to some problems with HS WD sample completeness estimations. It is clearly visible that the LF has unexpected plateau between 1.5 and 4 absolute bolometric magnitudes. There is nothing similar visible in a LF built only for non-DA WDs. The plateau might be real but we are concern that its existence can be connected to the problems with spectra calibration of the blue objects in SDSS DR4 data and lack of good stellar atmosphere models for the hottest DA white dwarfs.

Quantitative Spectroscopy of 24 A Supergiants in the Sculptor Galaxy NGC 300: Flux‐weighted Gravity–Luminosity Relationship, Metallicity, and Metallicity Gradient

A quantitative spectral analysis of 24 A supergiants in the Sculptor Group spiral galaxy NGC 300 at a distance of 1.9 Mpc is presented. A new method is introduced to analyze low-resolution (~5 A) spectra, which yields metallicities accurate to 0.2 dex including the uncertainties arising from the errors in Teff (5%) and log g (0.2 dex). For the first time the stellar metallicity gradient based on elements such as titanium and iron in a galaxy beyond the Local Group is investigated. Solar metallicity is measured in the center and 0.3 solar in the outskirts and a logarithmic gradient of –0.08 dex kpc−1. An average reddening of E(B − V) ~ 0.12 mag is obtained, however, with a large variation from 0.07 to 0.24 mag. We also determine stellar radii, luminosities, and masses and discuss the evolutionary status. Finally, the observed relationship between absolute bolometric magnitudes Mbol and flux-weighted gravities gF = g/T4eff is investigated. At high temperatures the strength of the Balmer lines depends solely on the flux-weighted gravity, which allows a precise direct determination of log gF with an accuracy of 0.05-0.1 dex. We find a tight relationship between Mbol and log gF in agreement with stellar evolution theory. Combining these new results with previous work on Local Group galaxies, we obtain a new flux-weighted gravity-luminosity relationship (FGLR), which is very well defined and appears to be an excellent alternative tool to determine distances to galaxies.

THE BM Ori system. IV. A new component of the system

Cross correlations between observed and synthetic spectra are used to discover yet another satellite of BM Ori with the following characteristics: effective temperature Teff = 4000 K, radius R = 16R⊙, mass M = 1.8M⊙, spectral type K7 III, absolute bolometric stellar magnitude Mb = + 4m·0, axial rotation velocity V sini = 85 km/s, and relative luminosity 0.005 near the V band.

The distances of less-evolved planetary nebulae: a further test of statistical distance scales

It has recently been pointed out that a number of the methods used to determine planetary nebulae (PNe) distances may be appreciably in error. Whilst the scales of Zhang (1995), Bensby & Lundstrom (2001) and others are appropriate for higher radio brightness temperatures TB, those of Phillips and Daub are more relevant where TB is small. We note, in the following, that the absolute bolometric magnitudes of less-evolved PNe are likely to be similar. The mean value of 〈MBOL〉 can therefore be used to constrain PNe distances D, and confirm the distance scales for higher TB outflows. We have used this procedure to evaluate distances to a further 47 PNe, and we find that the mean values of 〈D〉 are consistent with those of Cahn, Kaler & Stanghellini (1992), Zhang (1995), Phillips et al. (2004) and van de Steene & Zijlstra (1995). They are, as expected, inconsistent with the lower TB scale of Phillips (2002a).

Period-luminosity relation for M-type semiregular variables fromHipparcosparallaxes

We have studied the period–luminosity (P–L) relationships of oxygen-rich semiregular (SR) variables in several wavelength bands using Hipparcos parallaxes with an accuracy of better than 10 per cent. We have shown that there is a clear dependence on period of absolute magnitude in the U, B, V, R, IC, J, H, K, L, M, N, [12], [25], [60] and [100] bands, and that the slope of the linear Mλ– logP relation is a smooth function of wavelength. We point out that this relation can in principle be used to derive absolute bolometric magnitude as a function of period. The behaviour of the second periods of SR variables in the P–L relation in the V and K bands is also discussed.

A census of AGB stars in Local Group galaxies

Our photometric survey of Local Group galaxies, using a four filter technique based on the method of Wing (1971) allows the identification and subsequent characterization of their late-type stellar content. Two narrow band filters centred on molecular bands of TiO and CN allow us to distinguish between AGB stars of different chemistries (M-type (O-rich) and C-type (C-rich)). The faint dwarf spheroidal galaxy And II, a member of the M 31 subgroup, was surveyed. From photometry in V and i as well as in the narrow band filters TiO and CN we were able to identify 7 new AGB carbon stars, to derive their mean absolute � Miand bolometric magnitude Mbol, their luminosity function, and their spatial distribution. We are unable to establish the true C/M ratio because the few M stars of And II are overwhelmed by foreground Galactic M stars.

Distance of the hypernova SN 2002ap via the expanding photosphere method

New optical photometric and spectroscopic data of the bright hypernova SN 2002ap are presented. The obtained light curves as well as the optical spectra agree well with other published data series. The distance has been inferred by applying the Expanding Photosphere Method for the data around maximum. The derived 6.7 Mpc is in good agreement with recent photometric distances of M 74. However, the total (random plus systematic) uncertainty of the EPM-distance is at least ±4.5 Mpc (about 70%). The physical parameters of the SN have been determined via simplified analytic models of the light and velocity curves. It is confirmed that SN 2002ap was a less energetic hypernova, the kinetic energy was erg, and the reddening-free absolute bolometric magnitude reached -16.63 mag (corresponding to ), about 2 mag less than the prototype hypernova SN 1998bw.

Near-infrared photometry of 20 hipparcos carbon stars

Near-infrared JHK photometry was carried out for 20 carbon stars observed by the satellite Hipparcos. From the observations, bolometric corrections in the K band ( BC K ), apparent bolometric magnitudes ( m rmbo ) and effective temperatures ( T e ) of these stars were estimated. Combined with the trigonometric parallaxes measured by Hipparcos, the absolute bolometric magnitudes ( M bol) of some of the stars were obtained.