More Like this

1. Detailed Chemical Abundances for a Benchmark Sample of M Dwarfs from the APOGEE Survey

   https://doi.org/10.3847/1538-4357/ac4891  

   Souto, Diogo ; Cunha, Katia ; Smith, Verne V. ; Prieto, C. Allende ; Covey, Kevin ; García-Hernández, D. A. ; Holtzman, Jon A. ; Jönsson, Henrik ; Mahadevan, Suvrath ; Majewski, Steven R. ; et al ( March 2022 , The Astrophysical Journal)

   Abstract Individual chemical abundances for 14 elements (C, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, and Ni) are derived for a sample of M dwarfs using high-resolution, near-infrared H -band spectra from the Sloan Digital Sky Survey-IV/Apache Point Observatory Galactic Evolution Experiment (APOGEE) survey. The quantitative analysis included synthetic spectra computed with 1D LTE plane-parallel MARCS models using the APOGEE Data Release 17 line list to determine chemical abundances. The sample consists of 11 M dwarfs in binary systems with warmer FGK dwarf primaries and 10 measured interferometric angular diameters. To minimize atomic diffusion effects, [X/Fe] ratios are used to compare M dwarfs in binary systems and literature results for their warmer primary stars, indicating good agreement (<0.08 dex) for all studied elements. The mean abundance difference in primaries minus this work’s M dwarfs is −0.05 ± 0.03 dex. It indicates that M dwarfs in binary systems are a reliable way to calibrate empirical relationships. A comparison with abundance, effective temperature, and surface gravity results from the APOGEE Stellar Parameter and Chemical Abundances Pipeline (ASPCAP) Data Release 16 finds a systematic offset of [M/H], T eff , log g = +0.21 dex, −50 K, and 0.30 dex, respectively, although ASPCAP [X/Fe] ratios are generally consistent with this study. The metallicities of the M dwarfs cover the range of [Fe/H] = −0.9 to +0.4 and are used to investigate Galactic chemical evolution via trends of [X/Fe] as a function of [Fe/H]. The behavior of the various elemental abundances [X/Fe] versus [Fe/H] agrees well with the corresponding trends derived from warmer FGK dwarfs, demonstrating that the APOGEE spectra can be used to examine Galactic chemical evolution using large samples of selected M dwarfs. 

   more » « less
2. The Galactic chemical evolution of phosphorus observed with IGRINS

   https://doi.org/10.1051/0004-6361/202244724  

   Nandakumar, G. ; Ryde, N. ; Montelius, M. ; Thorsbro, B. ; Jönsson, H. ; Mace, G. ( December 2022 , Astronomy & Astrophysics)

   Context. Phosphorus (P) is considered to be one of the key elements for life, making it an important element to look for in the abundance analysis of spectra of stellar systems. Yet, only a select number of spectroscopic studies exist to estimate the phosphorus abundances and investigate its trend across a range of metallicities. This is due to the lack of good phosphorus lines in the optical wavelength region and the requirement of careful manual analysis of the blended phosphorus lines in near-infrared H-band spectra obtained with individual observations and surveys such as the Apache Point Observatory Galactic Evolution Experiment (APOGEE). Aims. Based on a consistent and systematic analysis of high-resolution, near-infrared Immersion GRating INfrared Spectrograph (IGRINS) spectra of 38 K giant stars in the Solar neighborhood, we present and investigate the phosphorus abundance trend in the metallicity range of −1.2 dex < [Fe/H] < 0.4 dex. Furthermore, we compare this trend with the available chemical evolution models to shed some light on the origin and evolution of phosphorus. Methods. We have observed full H - and K -band spectra at a spectral resolving power of R = 45 000 with IGRINS mounted on the Gemini South telescope, the Discovery Channel Telescope, and the Harlan J Smith Telescope at McDonald Observatory. Abundances were determined from spectral lines by modeling the synthetic spectrum that best matches the observed spectrum by χ 2 minimization. For this task, we used the Spectroscopy Made Easy (SME) tool in combination with one-dimensional (1D) Model Atmospheres in a Radiative and Convective Scheme (MARCS) stellar atmosphere models. The investigated sample of stars have reliable stellar parameters estimated using optical FIber-fed Echelle Spectrograph (FIES) spectra obtained in a previous study of a set of stars called Giants in the Local Disk (GILD). In order to determine the phosphorus abundances from the 16482.92 Å phosphorus line, we needed to take special care blending the CO( v = 7−4) line. With the stellar parameters known, we thus determined the C, N, and O abundances from atomic carbon and a range of nonblended molecular lines (CO, CN, and OH) which are plentiful in the H-band region of K giant stars, assuring an appropriate modeling of the blending CO( v = 7−4) line. Results. We present the [P/Fe] versus [Fe/H] trend for K giant stars in the metallicity range of −1.2 dex < [Fe/H] < 0.4 dex and enhanced phosphorus abundances for two metal-poor s-rich stars. We find that our trend matches well with the compiled literature sample of prominently dwarf stars and the limited number of giant stars. Our trend is found to be higher by ~0.05−0.1 dex compared to the theoretical chemical evolution trend resulting from the core collapse supernova (type II) of massive stars with the phosphorus yields arbitrarily increased by a factor of 2.75. Thus the enhancement factor might need to be ~0.05−0.1 dex higher to match our trend. We also find an empirically determined primary behavior for phosphorus. Furthermore, the phosphorus abundance is found to be elevated by ~0.6−0.9 dex in the two s-enriched stars compared to the theoretical chemical evolution trend. 

   more » « less
3. Benchmarking the fundamental parameters of Ap stars with optical long-baseline interferometric measurements

   https://doi.org/10.1051/0004-6361/202038753  

   Perraut, K. ; Cunha, M. ; Romanovskaya, A. ; Shulyak, D. ; Ryabchikova, T. ; Hocdé, V. ; Nardetto, N. ; Mourard, D. ; Meilland, A. ; Morand, F. ; et al ( October 2020 , Astronomy & Astrophysics)

   null (Ed.)

   Context. The variety of physical processes at play in chemically peculiar stars makes it difficult to determine their fundamental parameters. In particular, for the magnetic ones, called Ap stars, the strong magnetic fields and the induced spotted stellar surfaces may lead to biased effective temperatures when these values are derived through spectro-photometry. Aims. We propose to benefit from the exquisite angular resolution provided by long-baseline interferometry in the visible to determine the accurate angular diameters of a number of Ap stars, and thus estimate their radii by a method that is as independent as possible of atmospheric models. Methods. We used the visible spectrograph VEGA at the CHARA interferometric array to complete the sample of Ap stars currently observable with this technique. We estimated the angular diameter and radius of six new targets. We estimated their bolometric flux based solely on observational spectroscopic and photometric data to derive nearly model-independent luminosities and effective temperatures. Results. We extend to 14 the number of Ap stars for which interferometric angular diameters have been measured. The fundamental parameters we derived for the complete Ap sample are compared with those obtained through a self-consistent spectroscopic analysis. Based on a model fitting approach of high-resolution spectra and spectro-photometric observations over a wide wavelength range, this method takes into account the anomalous chemical composition of the atmospheres and the inhomogeneous vertical distribution for different chemical elements. Regarding both the radii and the effective temperatures, the derived values from our interferometric observations and from self-consistent modelling are consistent within better than 2 σ for nine targets out of ten. We thus benchmark nine Ap stars for effective temperatures ranging from 7200 and 9100 K, and luminosities ranging between 7 L ⊙ and 86 L ⊙ . Conclusions. These results will be key for the future derivation of accurate radii and other fundamental parameters of fainter peculiar stars for which both the sensitivity and the angular resolution of the current interferometers are not sufficient. Within the context of the observations of Ap stars with the Transiting Exoplanet Survey Satellite (TESS), these interferometric measurements are crucial for testing the mechanism of pulsation excitation at work in these peculiar stars. In particular, our interferometric measurements provide accurate locations in the Hertzsprung-Russell diagram for hot Ap stars among which pulsations may be searched for with TESS, putting to test the blue edge of the theoretical instability strip. These accurate locations could be used to derive masses and ages of these stars through a specific grid of models, and to test correlations between the properties of these peculiar stars and their evolutionary state. 

   more » « less
4. Kinematics of the Central Stars Powering Bowshock Nebulae and the Large Multiplicity Fraction of Runaway OB Stars

   https://doi.org/10.3847/1538-3881/ac7f2b  

   Kobulnicky, Henry A. ; Chick, William T. ( August 2022 , The Astronomical Journal)

   OB stars powering stellar bowshock nebulae (SBNe) have been presumed to have large peculiar velocities. We measured peculiar velocities of SBN central stars to assess their kinematics relative to the general O-star population using Gaia EDR3 data for 267 SBN central stars and a sample of 455 Galactic O stars to derive projected velocitiesv_2D. For a subset of each sample, we obtained new optical spectroscopy to measure radial velocities and identify multiple-star systems. We find a minimum multiplicity fraction of 36% ± 6% among SBN central stars, consistent with >28% among runaway Galactic O stars. The large multiplicity fraction among runaways implicates very efficient dynamical ejection rather than binary-supernova origins. The medianv_2Dof SBN central stars isv_2D= 14.6 km s⁻¹, larger than the medianv_2D= 11.4 km s⁻¹for non-bowshock O stars. Central stars of SBNe have a runaway (v_2D> 25 km s⁻¹) fraction of 24${}_{-7}^{+9}$%, consistent with the${22}_{-3}^{+3}$% for control-sample O stars. Most (76%) SBNe central stars are not runaways. Our analysis of alignment (Δ_PA) between the nebular morphological andv_2Dkinematic position angles reveals two populations: a highly aligned (σ_PA= 25°) population that includes stars with the largestv_2D(31% of the sample) and a random (nonaligned) population (69%). SBNe that lie within or near Hiiregions comprise a larger fraction of this latter component than SBNe in isolated environments, implicating localized ISM flows as a factor shaping their orientations and morphologies. We outline a new conceptual approach to computing the solar local standard of rest motion, yielding [U_⊙,V_⊙,W_⊙] = [5.5, 7.5,4.5] km s⁻¹.

    

   more » « less
5. Light elements Na and Al in 58 bulge spheroid stars from APOGEE

   https://doi.org/10.1093/mnras/stad2888  

   Barbuy, B. ; Friaça, A. C. S. ; Ernandes, H. ; Moura, T. ; Masseron, T. ; Cunha, K. ; Smith, V. V. ; Souto, D. ; Pérez-Villegas, A. ; Souza, S. O. ; et al ( September 2023 , Monthly Notices of the Royal Astronomical Society)

   We identified a sample of 58 candidate stars with metallicity [Fe/H] ≲ −0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20 per cent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H] ≲ −1.0. For the lower-metallicity end ([Fe/H < −2.5), hypernovae are assumed to be the main contributor to yields.

    

   more » « less