scholarly journals The flux-weighted gravity-luminosity relation of Galactic classical Cepheids

2020 ◽  
Vol 640 ◽  
pp. A113
Author(s):  
M. A. T. Groenewegen
Keyword(s):  
High Resolution ◽  
Effective Temperature ◽  
Spectroscopic Studies ◽  
High Resolution Spectroscopy ◽  
Spectral Energy ◽  
Pulsation Period ◽  
Instability Strip ◽  
Energy Distributions ◽  
Classical Cepheids ◽  
Good Agreement

The flux-weighted gravity-luminosity relation (FWGLR) is investigated for a sample of 477 classical Cepheids (CCs), including stars that have been classified in the literature as such but are probably not. The luminosities are taken from the literature, based on the fitting of the spectral energy distributions (SEDs) assuming a certain distance and reddening. The flux-weighted gravity (FWG) is taken from gravity and effective temperature determinations in the literature based on high-resolution spectroscopy. There is a very good agreement between the theoretically predicted and observed FWG versus pulsation period relation that could serve in estimating the FWG (and log g) in spectroscopic studies with a precision of 0.1 dex. As was known in the literature, the theoretically predicted FWGLR relation for CCs is very tight and is not very sensitive to metallicity (at least for LMC and solar values), rotation rate, and crossing of the instability strip. The observed relation has a slightly different slope and shows more scatter (0.54 dex). This is due both to uncertainties in the distances and to the pulsation phase averaged FWG values. Data from future Gaia data releases should reduce these errors, and then the FWGLR could serve as a powerful tool in Cepheid studies.

scholarly journals Analysing the spectral energy distributions of Galactic classical Cepheids

2020 ◽  
Vol 635 ◽  
pp. A33 ◽  
Author(s):  
M. A. T. Groenewegen
Keyword(s):  
Near Infrared ◽  
Three Dimensional ◽  
Far Infrared ◽  
Spectral Energy ◽  
Spectral Energy Distributions ◽  
Instability Strip ◽  
Energy Distributions ◽  
Infrared Excess ◽  
Mid Infrared ◽  
Classical Cepheids

Spectral energy distributions (SEDs) were constructed for a sample of 477 classical Cepheids (CCs); including stars that have been classified in the literature as such but are probably not. The SEDs were fitted with a dust radiative transfer code. Four stars showed a large mid- or far-infrared excess and the fitting then included a dust component. These comprise the well-known case of RS Pup, and three stars that are (likely) Type-II Cepheids (T2Cs), AU Peg, QQ Per, and FQ Lac. The infrared excess in FQ Lac is reported for the first time in this work. The remainder of the sample was fitted with a stellar photosphere to derive the best-fitting luminosity and effective temperature. Distance and reddening were taken from the literature. The stars were plotted in a Hertzsprung-Russell diagram (HRD) and compared to evolutionary tracks for Cepheids and theoretical instability strips. For the large majority of stars, the position in the HRD is consistent with the instability strip for a CC or T2C. About 5% of the stars are outliers in the sense that they are much hotter or cooler than expected. A comparison to effective temperatures derived from spectroscopy suggests in some cases that the photometrically derived temperature is not correct and that this is likely linked to an incorrectly adopted reddening. Two three-dimensional reddening models have been used to derive alternative estimates of the reddening for the sample. There are significant systematic differences between the two estimates with a non-negligible scatter. In this work the presence of a small near-infrared (NIR) excess, as has been proposed in the literature for a few well-known Cepheids, is investigated. Firstly, this was done by using a sample of about a dozen stars for which a mid-infrared spectrum is available. This data is particularly constraining as the shape of the observed spectrum should match that of the photosphere and any dust spectrum, both dust continuum and any spectral features of, for example, silicates or aluminium oxide. This comparison provides constraints on the dust composition, in agreement with a previous work in the literature. Secondly, the SEDs of all stars were fitted with a dust model to see if a statistically significant better fit could be obtained. The results were compared to recent work. Eight new candidates for exhibiting a NIR excess are proposed, solely based on the photometric SEDs. Obtaining mid-infrared spectra would be needed to confirm this excess. Finally, period-bolometric luminosity and period-radius relations are presented for samples of over 370 fundamental-mode CCs.

scholarly journals V363 Cassiopeiae: a new lithium-rich Galactic Cepheid

2020 ◽  
Vol 639 ◽  
pp. L4 ◽  
Author(s):  
G. Catanzaro ◽  
V. Ripepi ◽  
G. Clementini ◽  
F. Cusano ◽  
G. De Somma ◽  
...  
Keyword(s):  
Main Sequence ◽  
High Resolution Spectroscopy ◽  
Pulsation Period ◽  
Historical Time ◽  
Instability Strip ◽  
Lithium Abundance ◽  
Classical Cepheids ◽  
Astrophysical Objects ◽  
Metal Abundances

Context. Classical Cepheids (DCEPs) are important astrophysical objects not only as standard candles in the determination of the cosmic distance ladder, but also as a testbed for the stellar evolution theory. This is based on the strict connection between their pulsation (period(s) and amplitudes) and stellar parameters (luminosity, mass, effective temperature, and metallicity). Aims. We examine the nature of the Galactic DCEP V363 Cas and other DCEPs that show cosmic abundances of lithium in their atmospheres. Methods. We collected three epochs of high-resolution spectroscopy for V363 Cas with HARPS-N at the TNG. We measured accurate stellar parameters: the effective temperatures, gravities, microturbulences, radial velocities, and metal abundances. Results. We detected a lithium abundance of A(Li) = 2.86 ± 0.10 dex, along with iron, carbon, and oxygen abundances of [Fe/H] = −0.30 ± 0.12 dex, [C/H] = −0.06 ± 0.15 dex, and [O/H] = 0.00 ± 0.12 dex. V363 Cas is the fifth of the Milky Way DCEPs to exhibit a Li-rich feature. An analysis of historical time-series spanning a 100-year interval shows that the period of V363 Cas is increasing, with a sharp acceleration after HJD = 2 453 000 days. This is a clear indication of a first crossing of the instability strip. Conclusions. Our results favour the scenario in which the five Galactic Li-rich DCEPs are on their first crossing of the instability strip and have had slowly rotating progenitors during their main-sequence phase.

The high-resolution spectroscopy of dissociating molecules

1990 ◽  
Vol 332 (1625) ◽  
pp. 297-307 ◽  
Keyword(s):  
High Resolution ◽  
Energy Flow ◽  
Energy State ◽  
Reaction Dynamics ◽  
Theoretical Models ◽  
Spectroscopic Studies ◽  
High Resolution Spectroscopy ◽  
Bond Breaking ◽  
Vibrational Levels ◽  
Dynamical Constraints

Results from spectroscopic studies of the vibrational levels of dissociating molecules and from state-selected, state-resolved photofragmentation spectroscopy are presented. The extent of energy flow among the modes of a molecule is explored through the couplings, or lack thereof, revealed by high-resolution spectroscopy. The dynamics of energy flow during bond breaking are revealed by photofragment excitation spectroscopy and by product energy state distributions. These completely resolved data provide sensitive tests of dynamical constraints such as vibrational or rotational adiabaticity and thus of theoretical models for unimolecular reaction dynamics.

scholarly journals Chemical analysis of NGC 6528: one of the most metal-rich bulge globular clusters

2018 ◽  
Vol 620 ◽  
pp. A96 ◽  
Author(s):  
C. Muñoz ◽  
D. Geisler ◽  
S. Villanova ◽  
I. Saviane ◽  
C. C. Cortés ◽  
...  
Keyword(s):  
High Resolution ◽  
Chemical Analysis ◽  
Iron Content ◽  
Globular Clusters ◽  
Chemical Characterization ◽  
Heavy Elements ◽  
High Resolution Spectroscopy ◽  
Origin And Evolution ◽  
Red Giant ◽  
Good Agreement

Context. The bulge globular clusters (GCs) are key tracers of the bulge, a central and ancient component of our Galaxy. It is essential to understand their formation and evolution to study that of the bulge, as well as their relationship with the other Galactic GC systems (halo and disk GCs). High-resolution spectroscopy is a powerful tool for such studies, allowing us to obtain a detailed chemical characterization and kinematics of the clusters and to compare their chemical patterns with those of their halo and disk counterparts. Aims. Our main goals are to obtain detailed abundances for a sample of seven red giant members of NGC 6528 in order to characterize their chemical composition and study the relationship of this GC with the bulge, and with other bulge, halo, and disk GCs. Moreover, we analyze this cluster’s behavior associated with the multiple-populations phenomenon. Methods. We obtained the stellar parameters and chemical abundances of light elements (Na, Al), iron-peak elements (V, Cr, Mn, Fe, Co, Ni, Cu), α-elements (O, Mg, Si, Ca, Ti) and heavy elements (Zr, Ba, Eu) in seven red giant members of NGC 6528 using high-resolution spectroscopy from FLAMES-UVES. Results. In six stars of our sample we obtained a mean iron content of [Fe/H] = − 0.14 ± 0.03 dex, in good agreement with other studies. We found no significant internal iron spread. We detected one candidate variable star, which was excluded from the mean in iron content, and derived a metallicity in this star of [Fe/H] = − 0.55 ± 0.04 dex. Moreover, we found no extended O-Na anticorrelation but instead only an intrinsic Na spread. In addition, NGC 6528 does not exhibit a Mg-Al anticorrelation, and no significant spread in either Mg or Al. The α and iron-peak elements show good agreement with the bulge field star trend. The heavy elements are slightly dominated by the r-process. The chemical analysis suggests an origin and evolution similar to that of typical old Galactic bulge field stars. Finally, we find remarkable agreement in the chemical patterns of NGC 6528 and another bulge GC, NGC 6553, suggesting a similar origin and evolution.

scholarly journals Far-infrared Excesses in Classical Be Stars

2000 ◽  
Vol 175 ◽  
pp. 484-487 ◽  
Author(s):  
A.S. Miroshnichenko ◽  
K.S. Bjorkman
Keyword(s):  
High Resolution ◽  
Far Infrared ◽  
Infrared Emission ◽  
Circumstellar Dust ◽  
Spectral Energy ◽  
Be Stars ◽  
Spectral Energy Distributions ◽  
Energy Distributions ◽  
Rule Out

AbstractA sample of Be stars with large far-infrared excesses detected by IRAS is selected and their high-resolution IRAS images are examined. The far-infrared emission from most of them is marginally extended and is associated with the optical sources. Modeling of the stars’ spectral energy distributions allows us to rule out the infrared cirrus nature of the excesses. We suggest that the excesses are more likely due to circumstellar dust, possibly formed early in the evolution of the star.

scholarly journals The MACHO Project LMC Variable Star Inventory: Classical Cepheids, AGB Variables, and the Nine Million Star Color-Magnitude Diagram

1999 ◽  
Vol 190 ◽  
pp. 517-522
Author(s):  
D. R. Alves ◽  
A. Basu ◽  
K. H. Cook ◽  
D. L. Welch ◽  
Keyword(s):  
Theoretical Model ◽  
Variable Star ◽  
Instability Strip ◽  
Classical Cepheids ◽  
Magnitude Diagram ◽  
Iron Abundance ◽  
Low Metallicity ◽  
Low Mass ◽  
The Mean ◽  
Good Agreement

We measure the ratio of ~ 5M⊙ blue and red LMC supergiants (representative of classical Cepheids) using the MACHO Project's 9 million star color-magnitude diagram (9M CMD) of the LMC bar. We find b/r = 0.39, which favors the Z=0.008, 5M⊙ theoretical model of Schaerer et al. (1993) over that of Fagatto et al. (1994). Next, we examine the low mass (old) and low metallicity LMC field population (Pop. II). Features in the 9M CMD and properties of LMC field RRab variables are consistent with a mean iron abundance of [Fe/H] ≈ −1.5 dex for this population. Newly discovered post-HB/early-AGB Pop. II variables are identified in order to delineate the instability strip (IS). Good agreement with the theoretical IS of Bono et al. (1997) is found. We then compare the field RRab with newly identified RRab variables in the LMC clusters NGC 1898 and NGC 1835. We find the mean colors of these cluster RRab lie near the red and blue edges of the IS, respectively, which is similar to their respective (overall) red and blue HB morphologies. Since the field RRab lie on the red side of the IS, we infer the LMC field Pop. II is likely to have a red HB morphology.

scholarly journals JD 16 – Spectroscopy With Large Telescopes of Chemically Peculiar Stars: Preface

1998 ◽  
Vol 11 (2) ◽  
pp. 645-645
Author(s):  
M. Takada-Hidai ◽  
J. Zverko
Keyword(s):  
High Resolution ◽  
Spectroscopic Studies ◽  
High Resolution Spectroscopy ◽  
Stellar Spectroscopy ◽  
Chemically Peculiar ◽  
Peculiar Stars ◽  
New Findings ◽  
Chemically Peculiar Stars ◽  
Large Telescopes ◽  
Near Future

The Keck 10-m telescope has begun to produce many new findings in a field of stellar spectroscopy with the help of the High Resolution Spectrograph (HIRES). The other large telescopes such as the Subaru, VLT, and Gemini are now being constructed and expected to perform high-resolution spectroscopy in a near future within several years or so. These highresolution spectroscopic studies will be carried out based on studies which have been made mainly with existing telescopes with aperture smaller than 4 m.

scholarly journals Pulsation Period Change & Classical Cepheids: Probing the Details of Stellar Evolution

2014 ◽  
Vol 9 (S307) ◽  
pp. 224-225
Author(s):  
Hilding R. Neilson ◽  
Alexandra C. Bisol ◽  
Ed Guinan ◽  
Scott Engle
Keyword(s):  
Mass Loss ◽  
Real Time ◽  
Stellar Evolution ◽  
Stellar Mass ◽  
Period Change ◽  
Pulsation Period ◽  
Instability Strip ◽  
Loss Mechanism ◽  
Stellar Pulsation ◽  
Classical Cepheids

AbstractMeasurements of secular period change probe real-time stellar evolution of classical Cepheids making these measurements powerful constraints for stellar evolution models, especially when coupled with interferometric measurements. In this work, we present stellar evolution models and measured rates of period change for two Galactic Cepheids: Polaris and l Carinae, both important Cepheids for anchoring the Cepheid Leavitt law (period-luminosity relation). The combination of previously-measured parallaxes, interferometric angular diameters and rates of period change allows for predictions of Cepheid mass loss and stellar mass. Using the stellar evolution models, We find that l Car has a mass of about 9 M⊙ consistent with stellar pulsation models, but is not undergoing enhanced stellar mass loss. Conversely, the rate of period change for Polaris requires including enhanced mass-loss rates. We discuss what these different results imply for Cepheid evolution and the mass-loss mechanism on the Cepheid instability strip.

Science with the VO: Spectroscopic Studies of Herbig Ae/Be Stars

2012 ◽  
Vol 21 (3) ◽  
Author(s):  
D. Baines ◽  
J. Gonzalez ◽  
C. Arviset ◽  
I. Barbarisi ◽  
A. Laruelo ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Spectroscopic Studies ◽  
Spectral Energy ◽  
Analysis Tool ◽  
Be Stars ◽  
Energy Distributions ◽  
New Developments ◽  
Multi Wavelength ◽  
Opening Up ◽  
Comprehensive Study

AbstractThe Virtual Observatory (VO) is opening up new ways of exploiting the huge amount of data provided by the ever growing number of ground-based and space facilities. Using VOSpec, a multi-wavelength spectral analysis tool developed by the ESA-VO Team at ESAC, and new developments on scripting with VOSpec (VOScript), we have started to undertake a comprehensive study of spectroscopic and photometric data in the VO on Herbig Ae/Be stars. By studying line strengths, variabilities and spectral energy distributions, from the X-ray to sub-millimeter ranges, we aim to gain insights into processes and disk properties of a large sample of these objects. This paper presents initial findings of the spectroscopic analysis and initial spectral energy distribution classifications.

Sign in / Sign up

Export Citation Format

Share Document