Search

We present an UV spectrograph with an in-vacuum resolution R=λ/Δλ≈20000 covering the 70-400 nm wavelength range with an echelle configuration. The instrument is now in the assembly, test and verification phase, as a milestone of the project LAPSUS (LAboratory Plasma Spectroscopy for Ultraviolet Space) funded to the Italian National Institute for Nuclear Physics – Laboratori Nazionali del Sud (INFN-LNS) by the Italian Space Agency in 2020. The goal of the project is to build an experimental atomic database in the UV spectral range, useful to interpret astrophysical spectra acquired by space missions. For this purpose the LAPSUS spectrograph will be coupled to the plasma traps operating at INFN-LNS, in order to apply high resolution spectroscopy to the emission of laboratory plasmas resembling astrophysical environments.

The LAMOST-\textit{K}2 (L\textit{K}2) project, initiated in 2015, aims to collect low-resolution spectra of targets in the \textit{K}2 campaigns, similar to LAMOST-\textit{Kepler} project. By the end of 2018, a total of 126 L\textit{K}2 plates had been observed by LAMOST. After cross-matching the catalog of the LAMOST data release 6 (DR6) with that of the \textit{K}2 approved targets, we found 160,619 usable spectra of 84,012 objects, most of which had been observed more than once. The effective temperature, surface gravity, metallicity, and radial velocity from 129,974 spectra for 70,895 objects are derived through the LAMOST Stellar Parameter Pipeline (LASP). The internal uncertainties were estimated to be 81 K, 0.15 dex, 0.09 dex and 5 kms$^{-1}$, respectively, when derived from a spectrum with a signal-to-noise ratio in the $g$ band (SNR$_g$) of 10. These estimates are based on results for targets with multiple visits. The external accuracies were assessed by comparing the parameters of targets in common with the APOGEE and GAIA surveys, for which we generally found linear relationships. A final calibration is provided, combining external and internal uncertainties for giants and dwarfs, separately. We foresee that these spectroscopic data will be used widely in different research fields, especially in combination with \textit{K}2 photometry., 31 pages, 9 figures, 6 tables, accepted by ApJS

Phase \RNum{2} of the LAMOST-{\sl Kepler/K}2 survey (LK-MRS), initiated in 2018, aims at collecting medium-resolution spectra ($R\sim7,500$; hereafter MRS) for more than $50,000$ stars with multiple visits ($\sim60$ epochs) over a period of 5 years (2018 September to 2023 June). We selected 20 footprints distributed across the {\sl Kepler} field and six {\sl K}2 campaigns, with each plate containing a number of stars ranging from $\sim2,000$ to $\sim 3,000$. During the first year of observations, the LK-MRS has already collected $\sim280,000$ and $\sim369,000$ high-quality spectra in the blue and red wavelength range, respectively. The atmospheric parameters and radial velocities for $\sim259,000$ spectra of $21,053$ targets were successfully calculated by the LASP pipeline. The internal uncertainties for the effective temperature, surface gravity, metallicity, and radial velocity are found to be $100$\,K, $0.15$\,dex, $0.09$\,dex, and $1.00$\,km\,s$^{-1}$, respectively. We found $14,997$, $20,091$, and $1,514$ stars in common with the targets from the LAMOST low-resolution survey (LRS), GAIA and APOGEE, respectively, corresponding to a fraction of $\sim70\%$, $\sim95\%$ and $\sim7.2\%$. In general, the parameters derived from LK-MRS spectra are consistent with those obtained from the LRS and APOGEE spectra, but the scatter increases as the surface gravity decreases when comparing with the measurements from APOGEE. A large discrepancy is found with the GAIA values of the effective temperature. The comparisons of radial velocities of LK-MRS to GAIA and LK-MRS to APOGEE nearly follow an Gaussian distribution with a mean $\mu\sim1.10$ and $0.73$\,km\,s$^{-1}$, respectively., Comment: 24 pages, 15 figures, 4 tables, ApJS, accepted

The NASA Kepler satellite has provided unprecedented high duty-cycle, high-precision light curves for a large number of stars by continuously monitoring a field of view in Cygnus-Lyra region, leading to great progress in both discovering exoplanets and characterizing planet-hosting stars by means of asteroseismic methods. The asteroseismic survey allows the investigation of stars covering the whole H-R diagram. However, the low precision of effective temperatures and surface gravities in the KIC catalogue and the lack of information on chemical composition, metallicity and rotation rate prevent asteroseismic modeling, requiring spectroscopic observations for thousands of asteroseismic targets in the Kepler field in a homogeneous way.

The {\it Kepler} space mission and its {\it K2} extension provide photometric time series data with unprecedented accuracy. These data challenge our current understanding of the metallic-lined A stars (Am stars) for what concerns the onset of pulsations in their atmospheres. It turns out that the predictions of current diffusion models do not agree with observations. To understand this discrepancy, it is of crucial importance to obtain ground-based spectroscopic observations of Am stars in the {\it Kepler} and {\it K2} fields in order to determine the best estimates of the stellar parameters. In this paper, we present a detailed analysis of high-resolution spectroscopic data for seven stars previously classified as Am stars. We determine the effective temperatures, surface gravities, projected rotational velocities, microturbulent velocities and chemical abundances of these stars using spectral synthesis. These spectra were obtained with {\it CAOS}, a new instrument recently installed at the observing station of the Catania Astrophysical Observatory on Mt. Etna. Three stars have already been observed during quarters Q0-Q17, namely: HD\,180347, HD\,181206, and HD\,185658, while HD\,43509 was already observed during {\it K2} C0 campaign. We confirm that HD\,43509 and HD\,180347 are Am stars, while HD 52403, HD\,50766, HD\,58246, HD\,181206 and HD\,185658 are marginal Am stars. By means of non-LTE analysis, we derived oxygen abundances from O{\sc I}$\lambda$7771--5{\AA} triplet and we also discussed the results obtained with both non-LTE and LTE approaches., Comment: accepted in MNRAS main journal 13 pages, 11 figures, 3 tables. arXiv admin note: text overlap with arXiv:1404.0954

We present new spectroscopic observations of the early type, double-lined eclipsing binary V1441\,Aql. The radial velocities and the available photometric data obtained by $ASAS$ is analysed for deriving the parameters of the components. The components of V1441\,Aql are shown to be a B3\,IV primary with a mass M$_p$=8.02$\pm$0.51 M$_{\odot}$ and radius R$_p$=7.33$\pm$0.19 R$_{\odot}$ and a B9 III secondary with a mass M$_s$=1.92$\pm$0.14 M$_{\odot}$ and radius R$_s$=4.22$\pm$0.11 R$_{\odot}$. Our analyses show that V1441\,Aql is a double-contact system with rapidly rotating components. Based on the position of the components plotted on the theoretical Hertzsprung-Russell diagram, we estimate that the ages of V1441\,Aql is about 30\,Myr, neglecting the effects of mass exchange between the components. Using the UBVJHK magnitudes and interstellar absorption we estimated the mean distance to the system V1441\,Aql as 550$\pm$25\,pc., 21 Pages, 4 Figures, Accepted by NEW Astronomy

In this paper we present a detailed analysis of a sample of eight Am stars, four of them are in the Kepler field of view. We derive fundamental parameters for all observed stars, effective temperature, gravity, rotational and radial velocities, and chemical abundances by spectral synthesis method. Further, to place these stars in the HR diagram, we computed their luminosity. Two objects among our sample, namely HD114839 and HD179458 do not present the typical characteristic of Am stars, while for the others six we confirm their nature. The behavior of lithium abundance as a function of the temperature with respect the normal A-type stars has been also investigated, we do not find any difference between metallic and normal A stars. All the pulsating Am stars present in our sample (five

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) at the Xinglong observatory in China is a 4-m telescope equipped with 4,000 optical fibres. In 2010, we initiated the LAMOST-Kepler project which aimed at collecting low-resolution spectra of stars from the Kepler Input Catalog covering uniformly the Kepler field of view. The first round of the LAMOST-Kepler project has been completed in September 2014 resulting in more than 100,000 low-resolution spectra. We used those data to derive the effective temperature, the surface gravity, and the mean metallicity of our targets, as well as to detect fast rotators, and to identify emission-line stars. Our results are consistent with those reported in the literature and derived from high-resolution spectroscopy. The second round of the LAMOST-Kepler project will allow to improve the coverage of the Kepler field and to repeat observations of selected targets.

KIC 8677585 is a roAp star in the Kepler field which is unique in that there are four lowfrequency variations of unknown origin in addition to more than twenty high-frequency roAp modes. We analysed all available spectroscopy and conclude that the star has a constant radial velocity and most likely not a binary. We estimate its effective temperature to be Teff = 7300±200 K from high-dispersion spectra. We present an analysis of 829 d of Kepler short-cadence data which shows clear frequency and amplitude variations with a timescale of months. The dominant low-frequency peak at 3.142 d 1 has the same frequency and amplitude variation as one of the roAp modes. We therefore conclude that the low frequencies are oscillations in the roAp star itself, but the driving mechan ism is unknown. We find several frequency spacings among the roAp modes equal to the dominant low frequency, suggestive of nonlinear interactions. There is also a clear spacing of 37.2µHz which we interpret as the large separation and deduce that logg = 3.90 ± 0.03. Models with these parameters which take into account the effect of the magnetic field on the oscil lations are able to reproduce the observed range of roAp frequencies, but not the observed large separation. It is found that the properties of the oscillations are sensitive to the assumed stellar parameters and that a more detailed analysis is required. The fact that low frequencie s are closely coupled to the roAp frequencies calls into question our current understanding of pulsation in these stars.

We summarize the results of the completed first round of the LAMOST-Kepler project, and describe the status of its on-going second round. As a result of the first round of this project, the atmospheric parameters (Teff, log g, and [Fe/H]), the spectral classification (spectral type and luminosity class), and the radial velocities (RV) have been measured for 51,385 stars. For 4031 stars, we were able to measure the projected rotational velocity, while the minimum detectable v sin i was 120 km s-1. For 8821 stars with more than one observation, we computed the χ-square probability that the detected RV variations have a random occurrence. Finally, we classified 442 stars as chromospherically active on the basis of the analysis of their Hα and Ca II-IRT fluxes. All our results have been obtained from the low-resolution (R ∼ 1800) spectroscopic observations acquired with the LAMOST instrument. Based on observations collected with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) located at the Xinglong Observatory, China.

We show that the star KIC 4840675 observed by Kepler is composed of three stars with a rapidly rotating A-type star and two solar-type fainter companions. The A-type star is a δ Scuti variable with a dominant mode and many other modes of lower amplitude, including several low-frequency variations. The low-frequency variation with highest amplitude can be interpreted as rotational modulation with the light curve changing with time. However, the most interesting aspect of this star is a triplet of independent modes in the range 118–129 d −1 (1.4–1.5 mHz), which is far outside the range of typical δ Scuti frequencies. We discuss the possibility that these modes could be solar-like oscillations, oscillations of the roAp type or due to an unseen pulsating compact companion.

Delta Scuti (delta Sct) stars are opacity-driven pulsators with masses of 1.5-2.5M$_{\odot}$, their pulsations resulting from the varying ionization of helium. In less massive stars such as the Sun, convection transports mass and energy through the outer 30 per cent of the star and excites a rich spectrum of resonant acoustic modes. Based on the solar example, with no firm theoretical basis, models predict that the convective envelope in delta Sct stars extends only about 1 per cent of the radius, but with sufficient energy to excite solar-like oscillations. This was not observed before the Kepler mission, so the presence of a convective envelope in the models has been questioned. Here we report the detection of solar-like oscillations in the delta Sct star HD 187547, implying that surface convection operates efficiently in stars about twice as massive as the Sun, as the ad hoc models predicted., to appear as a Letter to Nature

We present an analysis of high-resolution spectra for two pulsating Am stars in the Kepler field. The stellar parameters derived in this way are important because parameters derived from narrow-band photometry may be affected by the strong metal lines in these stars. We analyse the Kepler time series of ten known Am stars and find that six of them clearly show δ Scuti pulsations. The other four appear to be non-pulsating. We derive fundamental parameters for all known pulsating Am stars from ground-based observations and also for the Kepler Am stars to investigate the location of the instability strip for pulsating Am stars. We find that there is not much difference between the Am-star instability strip and the δ Scuti instability strip. We find that the observed location of pulsating Am stars in the HR diagram does not agree with the location predicted from diffusion calculations.

Through the observational study of stellar pulsations, the internal structure of stars can be probed and theoretical models can be tested. The main sequence -γ Doradus (Dor) and δ Scuti (Sct) stars with masses 1.2–2.5 M⊙ are particularly interesting for asteroseismic study. The -γ Dor stars pulsate in high-order gravity (g) modes, with pulsational periods of order of one day. The δ Sct stars, on the other hand, show low-order g and pressure (p) modes with periods of order of 2 hours. Theory predicts the existence of ‘hybrid’ stars, i.e. stars pulsating in both types of modes, in an overlap region between the instability strips of -γ Dor and δ Sct stars in the Hertzsprung-Russell diagram. Hybrid stars are particularly interesting as the two types of modes probe different regions of the stellar interior and hence provide complementary model constraints. Before the advent of Kepler, only a few hybrid stars had been confirmed. The Kepler satellite is providing a true revolution in the study of and search for hybrid stars. Analysis of the first 50 days of Kepler data of hundreds of -γ Dor and δ Sct candidates reveals extremely rich frequency spectra, with most stars showing frequencies in both the δ Sct and -γ Dor frequency range. As these results show that there are practically no pure δ Sct or -γ Dor pulsators, a new observational classification scheme is proposed by Grigahcene et al. (2010). We present their results and characterize 234 stars in terms of δ Sct, -γ Dor, δ Sct/-γ Dor or -γ Dor/δ Sct hybrids (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

This study is an exploratory search to ascertain for the first time the detailed properties of σ Cas as a candidate pulsator of β Cephei type in view of future observing campaigns. This search is devoted to a precise characterization of the parameters of the star for verifying its location with respect to the β Cephei instability region and to a preliminary analysis of a possible spectral line-profile variability. The characterization of the parameters of the star was based both on spectroscopic observations carried out by us on October 2007 and literature data used to build its spectral energy distribution. The suspected pulsational variability of the star have been studied by analyzing the line-profile variability of the two spectral lines He i λ 5875.6 A and Si iii λ4552.6 A. The search for periodicity was performed by adopting the pixel-by-pixel method. From the analysis of the composite spectrum of σ Cas we derived the effective temperature and surface gravity. From literature values of distance, visual magnitude, bolometric correction and extinction we determined the luminosity and radius. By means of evolutionary tracks and isochrones we derived also mass and age. The values obtained pose σ Cas with a good certainty inside the β Cephei instability region. The line-profile variability analysis indicate a clear excess of oscillation power in the range 2–8 cycles d - 1 , with two prominent peaks at 3.00 and 5.32 cycles d - 1 , in the expected typical range of frequency of β Cephei pulsations. In this framework, it emerged that, besides the use of the canonical Si iii λ4552.6 A line for β Cephei pulsation studies, the He i λ5875.6 A line might be an additional suitable candidate for period and mode analysis in β Cephei stars.

We present the results of a study of a large sample of A and Am stars with spectral types from LAMOST and light curves from WASP. We find that, unlike normal A stars, $\delta$ Sct pulsations in Am stars are mostly confined to the effective temperature range 6900 $, Comment: Accepted for publication in MNRAS. 10 pages, 10 figures, 1 table

With the aim to test the present capability of the stellar surface lithium abundance in providing an estimation for the age of PMS stars, we analyze the case of the detached, double-lined, eclipsing binary system PAR 1802. For this system, the lithium age has been compared with the theoretical one, as estimated by applying a Bayesian analysis method on a large grid of stellar evolutionary models. The models have been computed for several values of chemical composition and mixing length, by means of the code FRANEC updated with the Trojan Horse reaction rates involving lithium burning.

In this paper, we present a multi-instrument analysis of the mercury-manganese star HD 49606. New spectroscopic observations have been obtained by us with Catania Astrophysical Observatory Spectropolarimeter (CAOS@OAC) and High Accuracy Radial Velocity Planet Searcher-North@Telescopio Nazionale Galileo (HARPS-N@TNG). Combining these observations with archive data coming from other instruments, we performed a comprehensive analysis of this star. We highlight the motion around the centre of mass of a binary system of SB1 type, and we calculate the fundamental parameters characterizing its orbit. We also speculate on the nature of the unseen component. From the fit of H β and H γ, we determined the effective temperature and gravity, while from a number of metal lines, we derive the rotational and microturbulent velocities. Regarding chemical composition, we found underabundances of helium, oxygen, magnesium, sulfur and nickel, solar composition for carbon and overabundances for all the other elements. In particular, mercury abundance is derived taking into account an isotopic mixture different from the terrestrial one. As to magnesium, silicon and phosphorus, we found a non-constant abundance with the optical depth, a result currently considered an evidence of stratification. Spectropolarimetric observations have been performed in the attempt to highlight the presence of a magnetic field, but no detection has been found.

We present light curves and periodograms for 27 stars in the young Upper Scorpius association (age=$11 \pm 1$\,Myr) obtained with the Kepler spacecraft. This association is only the second stellar grouping to host several pulsating pre-main sequence (PMS) stars which have been observed from space. From an analysis of the periodograms, we identify six $\delta$~Scuti variables and one $\gamma$~Doradus star. These are most likely PMS stars or else very close to the zero-age main sequence. Four of the $\delta$~Scuti variables were observed in short-cadence mode, which allows us to resolve the entire frequency spectrum. For these four stars, we are able to infer some qualitative information concerning their ages. For the remaining two $\delta$~Scuti stars, only long-cadence data are available, which means that some of the frequencies are likely to be aliases. One of the stars appears to be a rotational variable in a hierarchical triple system. This is a particularly important object, as it allows the possibility of an accurate mass determination when radial velocity observations become available. We also report on new high-resolution echelle spectra obtained for some of the stars of our sample., Comment: 19 pages, 9 figures. Accepted for publication on MNRAS

The abundance pattern of six stars classified as suspected chemically peculiar in the General Catalogue of Ap and Am stars by Renson has been derived to ascertain the real nature of these objects. Spectroscopic observations in the range λλ4800–5600 Å have been carried out at the stellar station of the INAF – Catania Astrophysical Observatory. Among the studied stars, for only three of them we confirmed their peculiarity, HD 155102 being a silicon star, HD 159082 a mercury–manganese star and HD 162132 a moderate metallic A-type star. The other three objects have chemical abundances not so different from the standard values derived in the literature for A-type stars and, furthermore, they do not show light variability. Hence, we suggest that they could be ruled out from Renson's catalogue.

We present a detailed study of the suspected Chemically Peculiar star HD 207538 based on high resolution spec- troscopy in the far Ultraviolet (1000-3350 A) and visible (4600-7000 A) ranges. The stellar abundance synthesis analysis was performed by using Kurucz's codes ATLAS9 and SYNTHE to compute the atmospheric model and the synthetic spectrum respectively. Observations were obtained with the Far Ultraviolet Spectroscopic Explorer ,t heInternational Ultraviolet Explorersatellites whereas the optical spectrum was collected with the ground-based Telescopio Nazionale Galileotelescope. With our analysis we refine the value of the rotational velocity to ve sin i = 42 3k m s 1 and the microturbulence velocity to = 8 1k m s 1 . The stellar abundances inferred in this study show that C, N, O, Al, Si, P, S and Mn are compatible with the standard solar abundances, within the experimental errors. On the other hand, Fe, Ni and Zn are definitively underabundant. We also show that the helium content is comparable to the typical abundance of B-type stars. Because this spectrum is rich in stellar and interstellar features, we computed simultaneously a synthetic spectrum of the stellar and interstellar lines in order to disentangle the dierent absorption contributions. We thus also determined the column densi- ties of several interstellar elements (Feii ,N i ,P ii ,H i ,H 2, HD, CO, Cli and Ari) present in the gas in front of the star. Although several components are present along this sightline, our results suggest the presence of some translucent interstellar gas among the diuse components. With this work, we demonstrate that it is possible to perform a stellar spectroscopic analysis from the far-UV to visible spectral range, with consistent results in both ranges within errors, based on one single atmosphere model.

We present ground-based spectra of early-type star candidates in the Local Group galaxies M 33 and NGC 6822 taken at the 4.2 m William Herschel Telescope (La Palma, Spain). Photospheric parameters Teff and log g were derived by LTE modeling of the Balmer lines. When possible, mass-loss rates were calculated from the Hα profiles computing emission and scattering in the wind with the method of Scuderi et al. (1992). Five hot star candidates were found in M 33, out of seven stars analyzed, and two out of three in NGC 6822.

We investigate the light variations of 15 Am stars using four years of high-precision photometry from the Kepler spacecraft and an additional 14 Am stars from the K2 Campaign 0 field. We find that most of the Am stars in the Kepler field have light curves characteristic of rotational modulation due to star spots. Of the 29 Am stars observed, 12 are {\delta} Scuti variables and one is a {\gamma} Doradus star. One star is an eclipsing binary and another was found to be a binary from time-delay measurements. Two Am stars show evidence for flares which are unlikely to be due to a cool companion. The fact that 10 out of 29 Am stars are rotational variables and that some may even flare strongly suggests that Am stars possess significant magnetic fields. This is contrary to the current understanding that the enhanced metallicity in these stars is due to diffusion in the absence of a magnetic field. The fact that so many stars are {\delta} Scuti variables is also at odds with the prediction of diffusion theory. We suggest that a viable alternative is that the metal enhancement could arise from accretion., Comment: 12 pages, 13 figures

The Kepler space mission provided near-continuous and high-precision photometry of about 207,000 stars, which can be used for asteroseismology. However, for successful seismic modelling it is equally important to have accurate stellar physical parameters. Therefore, supplementary ground-based data are needed. We report the results of the analysis of high-resolution spectroscopic data of A- and F-type stars from the Kepler field, which were obtained with the HERMES spectrograph on the Mercator telescope. We determined spectral types, atmospheric parameters and chemical abundances for a sample of 117 stars. Hydrogen Balmer, Fe I, and Fe II lines were used to derive effective temperatures, surface gravities, and microturbulent velocities. We determined chemical abundances and projected rotational velocities using a spectrum synthesis technique. The atmospheric parameters obtained were compared with those from the Kepler Input Catalogue (KIC), confirming that the KIC effective temperatures are underestimated for A stars. Effective temperatures calculated by spectral energy distribution fitting are in good agreement with those determined from the spectral line analysis. The analysed sample comprises stars with approximately solar chemical abundances, as well as chemically peculiar stars of the Am, Ap, and Lambda Boo types. The distribution of the projected rotational velocity, Vsini, is typical for A and F stars and ranges from 8 to about 280 km/s, with a mean of 134 km/s., Comment: Accepted for publication in MNRAS (22 pages, 6 tables)

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) at the Xinglong observatory in China is a new 4-m telescope equipped with 4,000 optical fibers. In 2010, we initiated the LAMOST-Kepler project. We requested to observe the full field-of-view of the nominal Kepler mission with the LAMOST to collect low-resolution spectra for as many objects from the KIC10 catalogue as possible. So far, 12 of the 14 requested LAMOST fields have been observed resulting in more than 68,000 low-resolution spectra. Our preliminary results show that the stellar parameters derived from the LAMOST spectra are in good agreement with those found in the literature based on high-resolution spectroscopy. The LAMOST data allows to distinguish dwarfs from giants and can provide the projected rotational velocity for very fast rotators., CoRoT Symposium 3 / Kepler KASC-7 joint meeting, Toulouse, July 2014. To be published by EPJ Web of Conferences

We derive some element abundances for the central star of the planetary nebula K648 from analysis of Hubble Space Telescope Faint Object Spectrograph spectra (1200–3300 A). Carbon is found to be approximately 4 times overabundant with respect to solar values, while oxygen is underabundant and silicon about solar, and He/H = 0.6. The stellar continuum indicates a reddening of E(B-V) = 0.08 and is well approximated by a synthetic model with Teff = 37,000 K and log g = 4.0, as found previously by Heber, Dreizler, & Werner. The scaling of the synthetic model with the measured UV flux indicates R = 1.3 R⊙, and thus log (L/L⊙) = 3.45, M = 0.62 M⊙, assuming a distance of D = 10.3 kpc. The C IV exhibits a wind profile, from which a terminal wind velocity of V∞ = 1600 ± 150 km s-1 is derived and a column density of Ni(C IV) = 6 ± 3 × 1015 cm-2. From ground-based spectra obtained at the William Hershel 4.2 m telescope we derive the first measurement of the expansion velocity for the nebula: Vexp([N II]) = 11.9 km s-1 and Vexp(Hα) = 16.7 km s-1. Combined with the nebular radius measured from HST imaging in our previous paper, the velocity yields an expansion age of the object Agekinematic ≥ 4270 yr. This value is slightly higher than predictions from post-AGB evolutionary models for a ≈0.6 M⊙ He-burning remnant. The photospheric overabundance of He and C, as well as the low luminosity of the central star, are consistent with a post-AGB object that experienced a late thermal pulse and consequent third dredge-up, and which is now in a luminosity-dip He-burning phase. The progenitor mass is fairly low.

In this paper we present new photometric and radial velocity data for the PMS $\delta$ Sct star H254, member of the young cluster IC 348. Photometric V,R$_C$,I$_C$ light curves were obtained at the Loiano and Asiago telescopes. The radial velocity data was acquired by means of the SARG@TNG spectrograph. High-resolution spectroscopy allowed us to derive precise stellar parameters and the chemical composition of the star, obtaining: T$_{\rm eff}$\,=\,6750\,$\pm$\,150 K; $\log g$\,=\,4.1\,$\pm$\,0.4 dex; [Fe/H]=-0.07$\pm$0.12 dex. Photometric and spectroscopic data were used to estimate the total absorption in the $V$ band A$_{\rm V}$=2.06$\pm$0.05 mag, in agreement with previous estimates. We adopted the technique of the difference in phase and amplitude between different photometric bands and radial velocities to verify that H254 is (definitely) pulsating in a radial mode. This occurrence allowed us to apply the CORS realization of the Baade--Wesselink method to obtain a value for the linear radius of H254 equal to 3.3$\pm$0.7 $R_\odot$. This result was used in conjunction with photometry and effective temperature to derive a distance estimate of 273$\pm$23 pc for H254, and, in turn for IC 348, the host cluster. This value is in agreement within the errors with the results derived from several past determinations and the evaluation obtained through the Hipparcos parallaxes. Finally, we derived the luminosity of H254 and studied its position in the Hertzsprung--Russell diagram. From this analysis it results that this $\delta$--Scuti occupies a position close to the red edge of the instability strip, pulsates in the fundamental mode, has a mass of about 2.2 $M_\odot$ and an age of 5$\pm$1 Myr, older than previous estimates., Comment: 12 pages. Accepted for publication on MNRAS

One of the most important astrophysical parameters characterizing stellar atmosphere is the surface gravity. By a direct knowledge of mass and radius of a star it is straightforward to compute also the gravity, but unfortunately this is possible only in a few cases. For most stars, the only chance we have to infer the surface gravity is based on the analysis of spectral features: lines and continuum. In this lecture we describe some of these methods, dealing with those most commonly used in the literature.

Before reaching our telescopes, stellar radiation passes through Earth's atmosphere. This interaction causes the formation of a number of telluric lines in registered stellar spectra. In this paper an atlas of atmospheric lines is reported. Observations have been carried out at the 91 cm cassegrain telescope of the M. G. Fracastoro observing station of the Catania Astrophysical Observatory equipped with a Czerney-Turner echelle spectrograph. The spectral region examined is between 6800 A and 7800 A. The possibility of using this atlas either to recognize telluric lines or as a wavelength calibration source is also discussed.

$\theta$ Cygni is an F3 spectral-type main-sequence star with visual magnitude V=4.48. This star was the brightest star observed by the original Kepler spacecraft mission. Short-cadence (58.8 s) photometric data using a custom aperture were obtained during Quarter 6 (June-September 2010) and subsequently in Quarters 8 and 12-17. We present analyses of the solar-like oscillations based on Q6 and Q8 data, identifying angular degree $l$ = 0, 1, and 2 oscillations in the range 1000-2700 microHz, with a large frequency separation of 83.9 plus/minus 0.4 microHz, and frequency with maximum amplitude 1829 plus/minus 54 microHz. We also present analyses of new ground-based spectroscopic observations, which, when combined with angular diameter measurements from interferometry and Hipparcos parallax, give T_eff = 6697 plus/minus 78 K, radius 1.49 plus/minus 0.03 solar radii, [Fe/H] = -0.02 plus/minus 0.06 dex, and log g = 4.23 plus/minus 0.03. We calculate stellar models matching the constraints using several methods, including using the Yale Rotating Evolution Code and the Asteroseismic Modeling Portal. The best-fit models have masses 1.35-1.39 solar masses and ages 1.0-1.6 Gyr. theta Cyg's T_eff and log g place it cooler than the red edge of the gamma Doradus instability region established from pre-Kepler ground-based observations, but just at the red edge derived from pulsation modeling. The pulsation models show gamma Dor gravity-mode pulsations driven by the convective-blocking mechanism, with frequencies of 1 to 3 cycles/day (11 to 33 microHz). However, gravity modes were not detected in the Kepler data, one signal at 1.776 cycles/day (20.56 microHz) may be attributable to a faint, possibly background, binary. Asteroseismic studies of theta Cyg and other A-F stars observed by Kepler and CoRoT, will help to improve stellar model physics and to test pulsation driving mechanisms., Comment: Accepted for Publication in The Astrophysical Journal, July 1, 2016

From a new set of spectroscopic observations we determined orbital parameters of six SB2 systems with one or both components being HgMn stars.We slightly refined the orbital periods for HD 32964, HD 173524, HD 174933 and HD 216494. Our results for HD 358 are in agreement with the previous literature studies. Regarding HD 33647, our orbital period is shorter than previous determinations. HD 173524 is a triple system. From the variations of the γ-velocity deduced from our and literature data, we refined the orbital period and we estimated the eccentricity of the third companion, for which we get e ≈ 0.13 and Porb = 36 ± 3 years. HD 191110 and HD 216494 seem to be the only synchronous SB2 within our sample. Following the hypothesis of rotational axes perpendicular to the orbital plane, we estimated the angle of the orbital plane to the line of sight. We identified in our spectra the signature of the Hβ of the third component of HD 216494 and we highlight a slight variation of the γ-velocity due to the presence of this component.Based on observations collected at the Stellar Station ``M. G. Fracastoro'' of the Catania Astrophysical Observatory, Italy.Appendix A is only available in electronic form at http://www.edpsciences.org

Although the importance of a correct abundance assumption in the determination of effective temperature and surface gravity of a star has been demonstrated in the literature, this determination is often still extremely simplified, neglecting the effects of non-solar chemical abundances. In this paper we show how the modeling of the profiles of Hδ and Hγ, commonly used as Teff and log g indicators, is affected when the chemical composition is far from the standard one. As a target for our study we selected the chemically peculiar star HR 6000. Comparing the observed and synthetic profiles of Hδ and Hγ we obtained Teff = 12 950 K and log g = 4.05; the atmospheric model has been computed with a metal opacity scale evaluated for (M/H) = −0.5 and He/H = 0. A number of FeII lines have been used to infer the rotational velocity (ve sini = 0k m s −1 )a nd the heliocentric radial velocity (RV = 0.67 km s −1 ). By requiring that the abundance of iron is independent of the 96 measured equivalent widths, we determined the microturubulence velocity (ξ = 0k m s −1 ). The abundance pattern coming from our study is similar to the one inferred from UV lines by Castelli et al. (1985), with the exception of O, Al, Si, Sc and Ni. Possible causes for these descrepancies are discussed. With respect to the Sun, we found the iron peak elements to be normal or overabundant and the light elements, with the exception of Na and P, to be extremely underabundant. We find that HR 6000 is one of the most He-underabundant among the chemically peculiar stars.

To try to understand the behavior of helium variability in Chemically Peculiar stars, we continued our on-going observational campaign started by Catanzaro, Leone & Catalano (1999). In this paper we present a new set of time resolved spectroscopic observations of the HeI5876 A line for a sample of 10 stars in the spectral range B3 - A2 and characterized by different overabundances. This line does not show variability in two stars: HD77350 and HD175156. It shows instead an equivalent width variation in phase with the Hipparcos light curve for two stars: HD79158 and HD196502. Antiphase variations have been found in 4 stars of our sample, namely: HD35502, HD124224, HD129174 and HD142990. Nothing we can say about HD115735 because of the constancy of Hipparcos photometric data, while no phase relation has been observed for HD90044. In the text we discuss the case of HD175156, according to photometric calibration and our spectroscopic observations we rule out the membership of this star to the main sequence chemically peculiar stars. We confirm the results obtained in the previous paper for which phase relations between light, spectral and magnetic variations are not dependent on stellar spectral type or peculiarity subclass.

With the aim of investigating the possible particular behavior of carbon in a sample of chemically peculiar stars of the main sequence without turning to modeling, we performed spectroscopic observations of three important and usually prominent single ionized carbon lines: 4267.261, 6578.052 and 6582.882 A. In addition, we observed a large number of standard stars in order to define a kind of normality strip, useful for comparing the observed trend for the peculiar stars. We paid particular attention to the problem of the determination of fundamental atmospheric parameters, especially for the chemically peculiar stars for which the abundance anomalies change the flux distribution in such a way that the classical photometric methods to infer effective temperatures and gravities parameter cannot be applied. Regarding CP stars, we found a normal carbon abundance in Hg–Mn, Si (with some exceptions) and He strong stars. He weak stars are normal too, but with a large spread out of the data around the mean value. A more complicated behavior has been noted in the group of SrCrEu stars: four out of seven show a strong overabundance, being the others normal.

We present blue spectra of massive stars in the Local Group galaxies NGC 6822 and M33. For all the targets, selected from our previous Hubble Space TelescopeWFPC2 photometry, no previous spectroscopic studies exist, to our knowledge, except for a bright Wolf-Rayet star in NGC 6822. Photospheric parameters Teff and gravity are derived by a model fit of the Balmer lines and multiband (UV to optical) photometry combined and are compared with evolutionary models. Inferred masses range from ≈ 7t o≈40 in the sample. From M, the spectroscopy, we classify the Wolf-Rayet star in NGC 6822 as WN3(-4), with no hydrogen. We estimate its progenitor mass of ≈ . For two stars in the NGC 6822 sample, our data are not sufficient to establish 40 10 M, whether they are foreground stars toward NGC 6822 or they belong to the galaxy.

For a sample of chemically peculiar stars, we report time-resolved measurements of the effective magnetic field which were obtained with the spectropolarimetry operating at the Catania Astrophysical Observatory . These observations are combined with data from the literature for better pointing out that periodic magnetic variability which characterises this class of stars. Periods given in the literature have been checked and, if possible, re-determined, not only by means of the magnetic measurements but referring also to the Hipparcos photometry. The variability of the effective magnetic field of the already known magnetic star 25 Sex is pointed out for the first time. As to the suspected magnetic chemically peculiar star EP UMa, our measurements confirm that this is really a magnetic star and we indicate a possible variability period. The accuracy of the variability period for CS Vir and FF Vir is improved. The suggestion that light variability is due to the re-distribution of ultraviolet flux towards the visible wavelengths in metal rich regions, which are not homogeneously distributed on the stellar surface, appears not always and straightly valid. Local line-blocking is certainly important in the case of CS Vir and a direct influence of the magnetic field on the infrared photometric variability cannot be ruled out for 25 Sex.