- ID:
- ivo://CDS.VizieR/J/A+A/654/A118
- Title:
- Vanadium measurements for 135 M dwarfs
- Short Name:
- J/A+A/654/A118
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- M-dwarf spectra are complex and notoriously difficult to model, posing challenges to understanding their photospheric properties and compositions in depth. Vanadium (V) is an iron-group element whose abundance supposedly closely tracks that of iron, but has origins that are not completely understood. Our aim is to characterize a series of neutral vanadium atomic absorption lines in the 800-910nm wavelength region of high signal-to-noise, high-resolution, telluric-corrected M-dwarf spectra from the CARMENES survey. Many of these lines are prominent and exhibit a distinctive broad and flat-bottom shape -- a result of hyperfine splitting (HFS). We investigate the potential and implications of these HFS-split lines for abundance analysis of cool stars. With standard spectral synthesis routines, as provided by the spectroscopy software iSpec and the latest atomic data (including HFS) available from the VALD3 database, we model these striking line profiles. We use them to measure V abundances of cool dwarfs. We determine V abundances for 135 early-M dwarfs (M0.0V to M3.5V) in the CARMENES guaranteed time observations sample. They exhibit a [V/Fe]-[Fe/H] trend consistent with that derived from nearby FG dwarfs. The tight (+/-0.1dex) correlation between [V/H] and [Fe/H] suggests the potential application of V as an alternative metallicity indicator in M dwarfs. We also show hints that a neglect to model HFS could partially explain the temperature correlation in V abundance measurements observed in previous studies of samples involving dwarf stars with Teff<=5300K. Our work suggests that HFS can impact certain absorption lines in cool photospheres more severely than in Sun-like ones. Therefore, we advocate that HFS should be carefully treated in abundance studies in stars cooler than ~5000 K. On the other hand, strong HFS split lines in high-resolution spectra present an opportunity for precision chemical analyses of large samples of cool stars. The V-to-Fe trends exhibited by the local M dwarfs continue to challenge theoretical models of V production in the Galaxy.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/234/25
- Title:
- Vanadium transitions in the spectrum of Arcturus
- Short Name:
- J/ApJS/234/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We derive a new abundance for vanadium in the bright, mildly metal-poor red giant Arcturus. This star has an excellent high-resolution spectral atlas and well-understood atmospheric parameters, and it displays a rich set of neutral vanadium lines that are available for abundance extraction. We employ a newly recorded set of laboratory FTS spectra to investigate any potential discrepancies in previously reported V I log(gf) values near 900nm. These new spectra support our earlier laboratory transition data and the calibration method utilized in that study. We then perform a synthetic spectrum analysis of weak V I features in Arcturus, deriving log{epsilon}(V)=3.54+/-0.01 ({sigma}=0.04) from 55 lines. There are no significant abundance trends with wavelength, line strength, or lower excitation energy.
- ID:
- ivo://CDS.VizieR/J/A+A/616/A58
- Title:
- Variability of the adiabatic parameter
- Short Name:
- J/A+A/616/A58
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Numerical models of the evolution of interstellar and intergalactic plasmas often assume that the adiabatic parameter {gamma} (the ratio of the specific heats) is constant (5/3 in monoatomic plasmas). However, {gamma} is determined by the total internal energy of the plasma, which depends on the ionic and excitation state of the plasma. Hence, the adiabatic parameter may not be constant across the range of temperatures available in the interstellar medium. We aim to carry out detailed simulations of the thermal evolution of plasmas with Maxwell-Boltzmann and non-thermal ({kappa} and n) electron distributions in order to determine the temperature variability of the total internal energy and of the adiabatic parameter. The plasma, composed of H, He, C, N, O, Ne, Mg, Si, S, and Fe atoms and ions, evolves under collisional ionization equilibrium conditions, from an initial temperature of 10^9^K. The calculations include electron impact ionization, radiative and dielectronic recombinations and line excitation. The ionization structure was calculated solving a system of 112 linear equations using the Gauss elimination method with scaled partial pivoting. Numerical integrations used in the calculation of ionization and excitation rates are carried out using the double-exponential over a semi-finite interval method. In both methods a precision of 10^-15^ is adopted. The total internal energy of the plasma is mainly dominated by the ionization energy for temperatures lower than 8x10^4^K with the excitation energy having a contribution of less than one percent. In thermal and non-thermal plasmas composed of H, He, and metals, the adiabatic parameter evolution is determined by the H and He ionizations leading to a profile in general having three transitions. However, for {kappa} distributed plasmas these three transitions are not observed for {kappa<15} and for {kappa<5} there are no transitions. In general, {gamma} varies from 1.01 to 5/3. Lookup tables of the {gamma} parameter are presented as supplementary material.
- ID:
- ivo://CDS.VizieR/J/MNRAS/345/609
- Title:
- Variability of the fine-structure constant
- Short Name:
- J/MNRAS/345/609
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have previously presented evidence for a varying fine-structure constant, {alpha}, in two independent samples of Keck/HIRES quasi-stellar object (QSO) absorption spectra. Here we present a detailed many-multiplet analysis of a third Keck/HIRES sample containing 78 absorption systems. We also re-analyse the previous samples, providing a total of 128 absorption systems over the redshift range 0.2<zabs<3.7.
- ID:
- ivo://CDS.VizieR/J/A+A/619/A152
- Title:
- Variation of MgHe line profile with temperature
- Short Name:
- J/A+A/619/A152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Line shapes of the magnesium resonance lines in white dwarf spectra are determined by the properties of magnesium atoms and the structure of the white dwarf atmosphere. Through their blanketing effect, these lines have a dominant influence on the model structure and thus on the determination from the spectra of other physical parameters that describe the stellar atmosphere and elemental abundances. In continuation of previous work on Mg+He lines in the UV, we present theoretical profiles of the resonance line of neutral Mg perturbed by He at the extreme density conditions found in the cool largely transparent atmosphere of DZ white dwarfs. We accurately determined the broadening of Mg by He in a unified theory of collisional line profiles using ab initio calculations of MgHe potential energies and transition matrix elements among the singlet electronic states that are involved for the observable spectral lines. We computed the shapes and line parameters of the Mg lines and studied their dependence on helium densities and temperatures. We present results over the full range of temperatures from 4000 to 12000K needed for input to stellar spectra models. Atmosphere models were constructed for a range of effective temperatures and surface gravities typical for cool DZ white dwarfs. We present synthetic spectra tracing the behavior of the Mg resonance line profiles under the low temperatures and high gas pressures prevalent in these atmospheres. The determination of accurate opacity data of magnesium resonance lines together with an improved atmosphere model code lead to a good fit of cool DZ white dwarf stars. The broadening of spectral lines by helium needs to be understood to accurately determine the H/He and Mg/He abundance ratio in DZ white dwarf atmospheres. We emphasize that no free potential parameters or ad hoc adjustments were used to calculate the line profiles.
- ID:
- ivo://CDS.VizieR/J/other/MmSAI/80.833
- Title:
- Variations of the fine-structure constant
- Short Name:
- J/other/MmSAI/80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Keck telescope's High Resolution Spectrograph (HIRES) has previously provided evidence for a smaller fine-structure constant, {alpha}, compared to the current laboratory value, in a sample of 143 quasar absorption systems: {Delta}{alpha}/{alpha}=(-0.57+/-0.11)10^-5^. The analysis was based on a variety of metal-ion transitions which, if alpha varies, experience different relative velocity shifts. This result is yet to be robustly contradicted, or confirmed, by measurements on other telescopes and spectrographs; it remains crucial to do so.
- ID:
- ivo://CDS.VizieR/J/A+AS/122/285
- Title:
- VCS Stark broadening tables for hydrogen
- Short Name:
- J/A+AS/122/285
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Stark profiles computed with the VCS theory are presented here for the Lyman, Balmer, Paschen, and Brackett series of hydrogen. They cover the series up to n=22 and a wide range of temperature and electron density. Both Doppler broadened profiles (as applicable to stellar atmospheres) and unbroadened profiles are given.
- ID:
- ivo://CDS.VizieR/J/A+A/572/A44
- Title:
- Vibrationally excited vinyl cyanide in Orion-KL
- Short Name:
- J/A+A/572/A44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Laboratory characterization (18-1893 GHz) and astronomical detection (IRAM-30m: 80-280GHz, Orion-KL) of CH_2_CHCN (vinyl cyanide) in its ground and vibrationally excited states. Improving the understanding of rotational spectra of vibrationally excited vinyl cyanide with new laboratory data and analysis. The laboratory results allow searching for these excited state transitions in the Orion-KL line survey. Furthermore, rotational lines of CH_2_CHCN contribute to the understanding of the physical and chemical properties of the cloud. Laboratory measurements of CH_2_CHCN made on several different frequency-modulated spectrometers were combined into a single broadband 50-1900GHz spectrum and its assignment was confirmed by Stark modulation spectra recorded in the 18-40GHz region and by ab-initio anharmonic force field calculations. For analyzing the emission lines of vinyl cyanide detected in Orion-KL we used the excitation and radiative transfer code (MADEX) at LTE conditions. Detailed characterisation of laboratory spectra of CH_2CHCN in 9 different excited vibrational states (v_11_=1, v_15_=1, v_11_=2, v_10_=1<==>(v_11_=1,v_15_=1), v_11_=3/v_15_=2/v_14_=1, (v_11_=1,v_10_=1)<==>(v_11_=2, v_15_=1), v_9_$=1, (v_11_=1,v_15_=2)<==>(v_10_=1, v_15_=1)<==>(v_11_=1,v_14_=1), and v_11_=4) and detection of transitions in the v_11_=2 and v_11_=3 states for the first time in Orion-KL, and of those in the v_10_=1<==>(v_11_=1,v_15_=1) dyad of states for the first time in space. The rotational transitions of the ground state of this molecule emerge from four cloud components of hot core nature which trace the physical and chemical conditions of high mass star forming regions in the Orion-KL Nebula. The lowest energy vibrationally excited states of vinyl cyanide such as v_11_=1 (at 328.5K), v_15_=1 (at 478.6K), v_11_=2 (at 657.8K), the v_10_=1<==>(v_11_=1,v_15_=1) dyad (at 806.4/809.9K), and v_11_=3 (at 987.9K) are populated under warm and dense conditions, so they probe the hottest parts of the Orion-KL source. The vibrational temperatures derived for the v_11_=1, v_11_=2, and v_15_=1 states are 252+/-76K, 242+/-121K, and 227+/-68K, respectively; all of them close to the mean kinetic temperature of the hot core component (210K). The total column density of CH_2_CHCN in the ground state is (3.0+/-0.9)x10^15^cm^-2^. We report the detection of methyl isocyanide (CH_3_NC) for the first time in Orion-KL and a tentative detection of vinyl isocyanide (CH_2_CHNC) and give column density ratios between the cyanide and isocyanide isomers obtaining a N(CH_3_NC)/N(CH_3_CN) ratio of 0.002. Laboratory characterisation of many previously unassigned vibrationally excited states of vinyl cyanide at microwave to THz frequencies allowed us to detect these molecular species in Orion-KL. Column density and rotational and vibrational temperatures for CH_2_CHCN in their ground and excited states, as well as for the isotopologues, have been constrained by means of a sample of more than 1000 lines in this survey.
- ID:
- ivo://CDS.VizieR/J/ApJS/214/18
- Title:
- VII log(gf) values, and V abundance in HD 84937
- Short Name:
- J/ApJS/214/18
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log{epsilon}(V)=3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H]=-2.08 from 68 lines, leading to a value of [V/Fe]=0.24.
- ID:
- ivo://CDS.VizieR/J/A+A/398/L11
- Title:
- Vinylacetylene millimeter-wave spectrum
- Short Name:
- J/A+A/398/L11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The pure rotational spectrum of the hydrocarbon vinylacetylene in its ground vibrational state has been investigated from 80 to 165 GHz, covering the rotational quantum numbers 8<=J=<18 and 0<=Ka<=17, n order to provide accurate rest frequencies for radioastronomical searches. Moreover, quantum chemical calculations of the dipole moment components {mu}a and {mu}b have been performed leading to the result {mu}a~0.4D. The value for the dipole moment component {mu}b is very low and lies in the range of several thousandth to a few hundredth of a Debye.
