EW Hα Research Articles

Accurate and Model-independent Radius Determination of Single FGK and M Dwarfs Using Gaia DR3 Data

Measuring fundamental stellar parameters is key to fully comprehending the evolution of stars. However, current theoretical models overpredict effective temperatures, and underpredict radii, compared to observations of K and M dwarfs (radius inflation problem). In this work, we have developed a model-independent method to infer precise radii of single FGK and M dwarfs using Gaia DR3 parallaxes and photometry, and used it to study the radius inflation problem. We calibrated nine surface brightness–color relations for the three Gaia magnitudes and colors using a sample of stars with angular diameter measurements. We achieved an accuracy of 4% in our angular diameter estimations, which Gaia’s parallaxes allow us to convert to physical radii. We validated our method by comparing our radius measurements with literature samples and the Gaia DR3 catalog, which confirmed the accuracy of our method and revealed systematic offsets in the Gaia measurements. Moreover, we used a sample with measured Hα equivalent width (Hα EW), a magnetic activity indicator, to study the radius inflation problem. We demonstrated that active stars have larger radii than inactive stars, showing that radius inflation is correlated with magnetic activity. We found a correlation between the radius inflation of active stars and Hα EW for the mass bin 0.5 < M[M ⊙] ≤ 0.6, but we found no correlation for lower masses. This could be due to lack of precision in our radius estimation or a physical reason. Radius measurements with smaller uncertainties are necessary to distinguish between the two scenarios.

Properties of Flare Events on M Stars from LAMOST Spectral Survey Based on Kepler and TESS Light Curves

A catalog of M stars has been published from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope data release 7 (LAMOST DR7). We cross-matched the LAMOST M catalog with Kepler, Kepler 2 (K2) and Transiting Exoplanet Survey Satellite (TESS) surveys. We obtained the light curves from the Kepler and TESS surveys. We detected 20,047 flare events from 4053 M stars and calculated their durations, amplitudes, and energies. We analyzed the distribution of the flare durations and energies. The distributions of flare duration for Kepler, K2 and TESS peak are at 3–3.5 hr, 4–6 hr and 1–1.5 hr, respectively. This may be the result of the different cadences for the three data sets. The highest regions of the flare energies of Kepler, K2 and TESS are 32–32.5, 32–32.5 and 31–31.5 erg in Log format, respectively. A linear relationship between flare duration and energy emerges from our analysis. The ratio of flare duration to total observational time is approximately 0.2%–0.3% for the Kepler, K2 and TESS surveys. The occurrence rate of a star with a flare event increases from the M0 to M4 subtypes. We also determined the spatial distribution of the flare rate of M stars in the Milky Way. It seems that the flare rate decreases as the vertical height increases. The power index of the flare energies is in the region of 1.53–2.32, which is similar to previous result for solar type star (2.0). Further, we examined the relationship between the flare amplitude and chromospheric intensity. The flare activity increases rapidly with the increase in the Hα EW at the lower values (less approximately 2 Å) and it increases slowly at the higher values.

Active galactic nuclei signatures in Red Geyser galaxies from Gemini GMOS-IFU observations

ABSTRACT Red Geysers are quiescent galaxies with galactic scale ionized outflows, likely due to low-luminosity active galactic nuclei (AGN). We used Gemini GMOS-IFU observations of the inner ∼1–3 kpc of nine Red Geysers selected from the MaNGA survey to study the gas ionization and kinematics. The emission-line ratios suggest the presence of Seyfert/LINER (Low Ionization Nuclear Emission Region) nuclei in all sources. Two galaxies show Hα equivalent width ( Hα EW) larger than 3 Å (indicative of AGN ionization) within an aperture 2 ${_{.}^{\prime\prime}}$5 of diameter (1.3–3.7 kpc at the distance of galaxies) for MaNGA data, while with the higher resolution GMOS data, four galaxies present Hα EW&amp;gt;3 Å within an aperture equal to the angular resolution (0.3–0.9 kpc). For two objects with GMOS-IFU data, the Hα EW is lower than 3 Å but larger than 1.5 Å, most probably due to a faint AGN. The spatially resolved electron density maps show values between 100 and 3000 cm −3 and are consistent with those determined in other studies. The large (MaNGA) and the nuclear scale (GMOS-IFU) gas velocity fields are misaligned, with a kinematic position angle difference between 12° and 60°. The [N ii] λ6583 emission-line profiles are asymmetrical, with blue wings on the redshifted side of the velocity field and red wings on the blueshifted side. Our results support previous indications that the gas in Red Geysers is ionized by an AGN, at least in their central region, with the presence of outflows, likely originating in a precessing accretion disc.

Calibration of the Hα Age–Activity Relation for M Dwarfs

Abstract In this work, we calibrate the relationship between Hα emission and M dwarf ages. We compile a sample of 892 M dwarfs with Hα equivalent width (Hα EW) measurements from the literature that are either comoving with a white dwarf of known age (21 stars) or in a known young association (871 stars). In this sample we identify 7 M dwarfs that are new candidate members of known associations. By dividing the stars into active and inactive categories according to their Hα EW and spectral type (SpT), we find that the fraction of active dwarfs decreases with increasing age, and the form of the decline depends on SpT. Using the compiled sample of age calibrators, we find that Hα EW and fractional Hα luminosity (L Hα /L bol) decrease with increasing age. Hα EW for SpT ≤ M7 decreases gradually up until ∼1 Gyr. For older ages, we found only two early M dwarfs that are both inactive and seem to continue the gradual decrease. We also found 14 mid-type M dwarfs, out of which 11 are inactive and present a significant decrease in Hα EW, suggesting that the magnetic activity decreases rapidly after ∼1 Gyr. We fit L Hα /L bol versus age with a broken power law and find an index of for ages ≲776 Myr. The index becomes much steeper at older ages, but a lack of field age-calibrators (≫1 Gyr) leaves this part of the relation far less constrained. Finally, from repeated independent measurements for the same stars, we find that 94% of them have a level of Hα EW variability ≤5 Å at young ages (&lt;1 Gyr).

Flare Rates, Rotation Periods, and Spectroscopic Activity Indicators of a Volume-complete Sample of Mid- to Late-M Dwarfs within 15 pc

Abstract We present a study of flare rates, rotation periods, and spectroscopic activity indicators of 125 single stars within 15 parsecs and with masses between 0.1 and 0.3 M ⊙ observed during the first year of the TESS mission, with the goal of elucidating the relationship between these various magnetically connected phenomena. We gathered multiepoch high-resolution spectra of each target, and we measured equivalent widths of the activity indicators helium I D3, Hα, and the calcium infrared triplet line at 8542.09 Å. We present 18 new rotation periods from MEarth photometry and 19 new rotation periods from TESS photometry. We present a catalog of 1392 flares. After correcting for sensitivity, we find the slope of the flare frequency distribution for all stars to have a standard value of α = 1.98 ± 0.02. We determine R 31.5, the rate of flares per day with energies above E = 3.16 × 1031 ergs in the TESS bandpass. We find that below a critical value of Hα EW = −0.71 Å, log R 31.5 increases linearly with increasing Hα emission; above this value, log R 31.5 declines rapidly. The stars divide into two groups: 26% have Hα in emission, high flare rates with typical values of log R 31.5 = −1.30 ± 0.08, and have Rossby numbers &lt;0.50. The remaining 74% show little to no Hα in emission and exhibit log R 31.5 &lt; −3.86, with the majority of these stars not showing a single flare during the TESS observations.

Star Formation in Isolated Dwarf Galaxies Hosting Tidal Debris: Extending the Dwarf–Dwarf Merger Sequence

Abstract Like massive galaxies, dwarf galaxies are expected to undergo major mergers with other dwarfs. However, the end state of these mergers and the role that merging plays in regulating dwarf star formation are uncertain. Using imaging from the Hyper Suprime-Cam Subaru Strategic Program, we construct a sample of dwarf–dwarf mergers and examine the star formation and host properties of the merging systems. These galaxies are selected via an automated detection algorithm from a sample of 6875 spectroscopically selected isolated dwarf galaxies at z &lt; 0.12 and from the Galaxy and Mass Assembly and Sloan Digital Sky Survey spectroscopic campaigns. We find a total tidal feature detection fraction of 3.29% (6.1% when considering only galaxies at z &lt; 0.05). The tidal feature detection fraction rises strongly as a function of star formation activity; 15%–20% of galaxies with extremely high Hα equivalent width (Hα EW &gt; 250 Å) show signs of tidal debris. Galaxies that host tidal debris are also systematically bluer than the average galaxy at fixed stellar mass. These findings extend the observed dwarf–dwarf merger sequence with a significant sample of dwarf galaxies, indicating that star formation triggered in mergers between dwarf galaxies continues after coalescence.

Relativistic supernova 2009bb exploded close to an atomic gas cloud

Context. The host galaxies of gamma-ray bursts (GRBs) have been claimed to have experienced a recent inflow of gas from the intergalactic medium. This is because their atomic gas distribution is not centred on their optical emission and because they are deficient in molecular gas given their high star formation rates (SFRs). Similar studies have not been conducted for host galaxies of relativistic supernovae (SNe), which may have similar progenitors. Aims. The potential similarity of the powering mechanisms of relativistic SNe and GRBs allowed us to make a prediction that relativistic SNe are born in environments similar to those of GRBs, that is, ones which are rich in atomic gas. Here we embark on testing this hypothesis by analysing the properties of the host galaxy NGC 3278 of the relativistic SN 2009bb. This is the first time the atomic gas properties of a relativistic SN host are provided and the first time resolved 21 cm-hydrogen-line (H I) information is provided for a host of an SN of any type in the context of the SN position. Methods. We obtained radio observations with the Australia Telescope Compact Array (ATCA) covering the H I line, and optical integral field unit spectroscopy observations with the Multi Unit Spectroscopic Explorer (MUSE) at the Very Large Telescope (VLT). Moreover, we analysed archival carbon monoxide (CO) and multi-wavelength data for this galaxy. Results. The atomic gas distribution of NGC 3278 is not centred on the optical galaxy centre, but instead around a third of atomic gas resides in the region close to the SN position. This galaxy has a few times lower atomic and molecular gas masses than predicted from its SFR. Its specific SFR (sSFR ≡ SFR/M*) is approximately two to three times higher than the main-sequence value, placing it at the higher end of the main sequence, towards starburst galaxies. SN 2009bb exploded close to the region with the highest SFR density and the lowest age, as evident from high Hα EW, corresponding to the age of the stellar population of ~5.5 Myr. Assuming this timescale was the lifetime of the progenitor star, its initial mass would have been close to ~36 M⊙. Conclusions. As for GRB hosts, the gas properties of NGC 3278 are consistent with a recent inflow of gas from the intergalactic medium, which explains the concentration of atomic gas close to the SN position and the enhanced SFR. Super-solar metallicity at the position of the SN (unlike for most GRBs) may mean that relativistic explosions signal a recent inflow of gas (and subsequent star formation), and their type (GRBs or SNe) is determined either (i) by the metallicity of the inflowing gas, so that metal-poor gas results in a GRB explosion and metal-rich gas (for example a minor merger with an evolved galaxy or re-accretion of expelled gas) results in a relativistic SN explosion without an accompanying GRB, or (ii) by the efficiency of gas mixing (efficient mixing for SN hosts leading to a quick disappearance of metal-poor regions), or (iii) by the type of the galaxy (more metal-rich galaxies would result in only a small fraction of star formation being fuelled by metal-poor gas).

ZFIRE: using Hα equivalent widths to investigate the in situ initial mass function at z ∼ 2

We use the ZFIRE (http://zfire.swinburne.edu.au) survey to investigate the high-mass slope of the initial mass function (IMF) for a mass-complete (⁠|$\mathrm{log_{10}({\it M}_*/\mathrm{M}_{\odot })\sim 9.3}$|⁠) sample of 102 star-forming galaxies at z ∼ 2 using their Hα equivalent widths (Hα EWs) and rest-frame optical colours. We compare dust-corrected Hα EW distributions with predictions of star formation histories (SFHs) from pegase.2 and starburst|$\scriptstyle{99}$| synthetic stellar population models. We find an excess of high Hα EW galaxies that are up to 0.3–0.5 dex above the model-predicted Salpeter IMF locus and the Hα EW distribution is much broader (10–500 Å) than can easily be explained by a simple monotonic SFH with a standard Salpeter-slope IMF. Though this discrepancy is somewhat alleviated when it is assumed that there is no relative attenuation difference between stars and nebular lines, the result is robust against observational biases, and no single IMF (i.e. non-Salpeter slope) can reproduce the data. We show using both spectral stacking and Monte Carlo simulations that starbursts cannot explain the EW distribution. We investigate other physical mechanisms including models with variations in stellar rotation, binary star evolution, metallicity and the IMF upper-mass cut-off. IMF variations and/or highly rotating extreme metal-poor stars (Z ∼ 0.1 Z⊙) with binary interactions are the most plausible explanations for our data. If the IMF varies, then the highest Hα EWs would require very shallow slopes (Γ > −1.0) with no one slope able to reproduce the data. Thus, the IMF would have to vary stochastically. We conclude that the stellar populations at z ≳ 2 show distinct differences from local populations and there is no simple physical model to explain the large variation in Hα EWs at z ∼ 2.

The Next Possible Outburst of P Cygni

AbstractOn the basis of long-term UBV observations of P Cygni, which were made by Eugene Kharadze and Nino Magalashvili between 1951-1983, is evident that P Cygni undergone reddening during those observations. P cygni is a LBV and a supernova impostor. Corrected on the reddening B-V color has values between about -0.4 (at the beginning of 1950-ies) and -0.1 (for the 1980-ies). It means that the star probably had earlier spectral type at the beginning of 20-th century and accordingly, we are witnesses of its evolutionary changes. It means also that on the HR diagram the star moves gradually to the instability strip of LBVs in Outburst. So, if the rate of the reddening of the P Cygni will the same in near future then the star will have the next eruption (or even supernova explosion) after approximately 80-120 years.The long (approximately 1500 d, 1160 d, 760 d, 580 d) quasi-periods and the shorter ones (approximatelly 130 d, 68 d and 15-18 days) were revealed using the above observations.We observed P Cygni on July 23 - October 20, 2014 with the 48 cm Cassegrain telescope and standard B,V,R,I filters. HD 228793 has been used as a comparison star. We revealed that during our observations the star underwent light variations with the mean amplitude of approximately 0.1 magnitudes in all pass-bands and the period of this change was approximately 68 days. There is also a relation between brightness and the Hα EW variability. Therefore, we think that the cause of this behavior may be a variability of rate of the stellar wind that is very strong in this star. Changes in the rate of the stellar wind, on the other hand, maybe due to the pulsation of the star. It seems that quasi-periods of the brightness variability are almost the exact multiples of each other which probably also indicates on pulsation of the star. According to the new photometric observations of 2014 the star continues reddening.

Spectroscopic study of Be-shell stars: 4 Her and 88 Her

We present an optical spectroscopic study based on 41 spectra of 4 Her and 32 spectra of 88 Her, obtained over a period of 6 months. We estimate the rotational velocity of these stars from HeI lines in the blue spectral region (4000–4500 Å). We find that these stars are likely to be rotating at a fractional critical rotation of ∼0.80. We measure the average Ip/Ic ratio to quantify the strength of the Hα line and obtain 1.63 for 4 Her and 2.06 for 88 Her. The radius of the Hα emission region is estimated to be Rd/R* ∼5.0, assuming a Keplerian disk. These stars are thus found to be fast rotators with a relatively small Hα emission region. We detect V/R variation of the Hα spectral line during the observed period. We re-estimate the periods for both stars and obtain a period of ∼46 d and its harmonic of 23.095 d for 4 Her, and a period of ∼86 d for 88 Her. As these two cases are shell stars with binaries and have low Hα EW with the emission region closer to the central star, the V/R variation and a change in period may be an effect of the binary on the circumstellar disk.

HR 5907: Discovery of the most rapidly rotating magnetic early B-type star by the MiMeS Collaboration★†

We report the discovery and analysis of a very strong magnetic field in the rapidly rotating early B-type star HR 5907, based on observations obtained as part of the Magnetism in Massive Stars (MiMeS) project. We infer a rotation period of 0.508 276+0.000 015−0.000 012 d from photometric and Hα EW measurements, making this the shortest period, non-degenerate, magnetic massive star known to date. From the comparison of IUE UV and optical spectroscopy with LTE bruce/kylie models we find a solid-angle integrated, uniform black-body temperature of 17 000 ± 1000 K, a projected rotational velocity of 290 ± 10 km s−1, an equatorial radius of 3.1 ± 0.2 R⊙, a stellar mass of 5.5 ± 0.5 M⊙, and an inclination angle of the rotation axis to our line-of-sight of 70 ± 10°. Our measurements of the longitudinal magnetic field, which vary between −500 and −2000 G, phase coherently with the rotation period and imply a surface dipole field strength of ∼15.7 kG. On the other hand, from fits to mean Least-Squares Deconvolved Stokes V line profiles we infer a dipole field strength of ∼10.4 kG. This disagreement may result from a magnetic configuration more complex than our model, and/or from the non-uniform helium surface abundance distribution. In either case we obtain a magnetic obliquity nearly aligned with the rotation axis (⁠⁠). Our optical spectroscopy also shows weak variability in carbon, silicon and nitrogen lines. The emission variability in hydrogen Balmer and Paschen lines indicates the presence of a dense, highly structured magnetosphere, interpreted as a centrifugally supported, magnetically confined circumstellar disc.

The Reliability of [C II] as a Star Formation Rate Indicator

AbstractWe present a calibration of the star formation rate (SFR) as a function of the [C II] 157.74 μm luminosity for a sample of 24 star-forming galaxies in the nearby universe. In order to calibrate the SFR against the line luminosity, we rely on both GALEX FUV data, which is an ideal tracer of the unobscured star formation, and Spitzer MIPS 24 μm, to probe the dust-enshrouded fraction of star formation. For this sample of normal star-forming galaxies, the [C II] luminosity correlates well with the star formation rate. However, the extension of this relation to more quiescent (Hα EW≤10 Å) or ultra luminous galaxies (L

A spectral study of the Be/X-ray binary LSI+61°303

New optical intermediate dispersion spectra of the periodic radio star LSI +361°303 are presented. The Hα emission line shows a typical hell absorption spectrum, which means that the primary of this Be/X-ray binary may be a nearly equator-on Be star. The Hα emission line profile and its variation are analyzed, and some parameters such as the Hα EW and V/R peak ratio change strongly near the radio maximum, and may exhibit periodic variability. Instead of having a wider minimum lasting for about half an orbital cycle as radio flux and V magnitude do, the Hα EW shows a deep minimum at phase ∼ 0.75. The accretion disk around the neutron star formed near its periastron passage is suggested to be responsible for the change when it eclipses the primary and its envelope.

Observations of the X-Ray Nova GRO J0422+32. II. Optical Spectra Approaching Quiescence

view Abstract Citations (24) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of the X-Ray Nova GRO J0422+32. II. Optical Spectra Approaching Quiescence Garcia, Michael R. ; Callanan, Paul J. ; McClintock, Jeffrey E. ; Zhao, Ping Abstract We present results obtained from a series of 5 Å resolution spectra of X-ray nova GRO J0422+32 obtained in 1993 October, when the system was approximately 2 mag above quiescence, with R ∼ 19. The data were obtained in an effort to measure the orbital radial velocity curve of the secondary, but detection of the narrow photospheric absorption lines needed to do this proved elusive. Instead we found wide absorption bands reminiscent of M star photospheric features. The parameters determined by fitting accretion disk line profiles (Smak profiles) to the Hα line are similar to those found in several strong black hole candidates. Measurements of the velocity of the Hα lines are consistent with an orbital period of 5.1 hr and a velocity semiamplitude of the primary of 34 + 6 km s '. These measurements, when combined with measurements of the velocity semiamplitude of the secondary made by others, indicate that the mass ratio q ∼ 0.09. If the secondary follows the empirical mass-radius relation found for cataclysmic variables, the low q implies a primary mass of Mx ∼ 5.6 Msun, and a rather low (face-on) inclination. The Hα EW is found to be modulated on the orbital period with a phasing that implies a partial eclipse of the disk by the secondary, but simultaneous R-band photometry shows no evidence for such an eclipse. Publication: The Astrophysical Journal Pub Date: April 1996 DOI: 10.1086/177021 arXiv: arXiv:astro-ph/9509021 Bibcode: 1996ApJ...460..932G Keywords: STARS: BINARIES: SPECTROSCOPIC; STARS: NOVAE; CATACLYSMIC VARIABLES; STARS: INDIVIDUAL ALPHANUMERIC: GRO J0422+32; X-RAYS: STARS; BLACK HOLE PHYSICS; Astrophysics E-Print: Accepted for ApJ, plain latex, 5 figures available as self-extracting uuendoced, compressed, tarfiles (from uufiles) full text sources arXiv | ADS | data products SIMBAD (7) Related Materials (1) Part 1: 1995ApJ...441..786C