scholarly journals Cepheid Metallicity in the Leavitt Law (C- MetaLL) survey: I. HARPS-N@TNG spectroscopy of 47 Classical Cepheid and 1 BL Her variables

2021 ◽  
Author(s):  
V Ripepi ◽  
G Catanzaro ◽  
R Molinaro ◽  
M Gatto ◽  
G De Somma ◽  
...  
Keyword(s):  
Hubble Constant ◽  
Zero Point ◽  
Spectral Lines ◽  
High Resolution Spectroscopy ◽  
Chemical Abundances ◽  
Classical Cepheids ◽  
Final Estimate ◽  
Metal Abundances ◽  
Extragalactic Distance Scale ◽  
Distance Indicators

Abstract Classical Cepheids (DCEPs) are the most important primary indicators of the extragalactic distance scale. Establishing the dependence on metallicity of their period–luminosity and period–Wesenheit (PLZ/PWZ) relations has deep consequences on the calibration of secondary distance indicators that lead to the final estimate of the Hubble constant (H0). We collected high-resolution spectroscopy for 47 DCEPs plus 1 BL Her variables with HARPS-N@TNG and derived accurate atmospheric parameters, radial velocities and metal abundances. We measured spectral lines for 29 species and characterized their chemical abundances, finding very good agreement with previous results. We re-determined the ephemerides for the program stars and measured their intensity-averaged magnitudes in the V, I, J, H, Ks bands. We complemented our sample with literature data and used the Gaia Early Data Release 3 (EDR3) to investigate the PLZ/PWZ relations for Galactic DCEPs in a variety of filter combinations. We find that the solution without any metallicity term is ruled out at more than the 5 σ level. Our best estimate for the metallicity dependence of the intercept of the PLKs, PWJKs, PWVKs and PWHVI relations with three parameters, is −0.456 ±0.099, −0.465 ±0.071, −0.459 ±0.107 and −0.366 ±0.089 mag/dex, respectively. These values are significantly larger than the recent literature. The present data are still inconclusive to establish whether or not also the slope of the relevant relationships depends on metallicity. Applying a correction to the standard zero point offset of the Gaia parallaxes has the same effect of reducing by ∼22% the size of the metallicity dependence on the intercept of the PLZ/PWZ relations.

scholarly journals The effect of metallicity on Cepheid period-luminosity relations from a Baade-Wesselink analysis of Cepheids in the Milky Way and Magellanic Clouds

2018 ◽  
Vol 620 ◽  
pp. A99 ◽  
Author(s):  
W. Gieren ◽  
J. Storm ◽  
P. Konorski ◽  
M. Górski ◽  
B. Pilecki ◽  
...  
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Hubble Constant ◽  
Zero Point ◽  
Small Sample ◽  
Type Method ◽  
Distance Analysis ◽  
Classical Cepheids ◽  
Extragalactic Distance Scale

Context. The extragalactic distance scale builds on the Cepheid period-luminosity (PL) relation. Decades of work have not yet convincingly established the sensitivity of the PL relation to metallicity. This currently prevents a determination of the Hubble constant accurate to 1% from the classical Cepheid-SN Ia method. Aims. In this paper we carry out a strictly differential comparison of the absolute PL relations obeyed by classical Cepheids in the Milky Way (MW), LMC, and SMC galaxies. Taking advantage of the substantial metallicity difference among the Cepheid populations in these three galaxies, we want to establish a possible systematic trend of the PL relation absolute zero point as a function of metallicity, and to determine the size of such an effect in the optical and near-infrared photometric bands. Methods. We used a IRSB Baade-Wesselink-type method to determine individual distances to the Cepheids in our samples in the MW, LMC, and SMC. For our analysis, we used a greatly enhanced sample of Cepheids in the SMC (31 stars) compared to the small sample (5 stars) available in our previous work. We used the distances to determine absolute Cepheid PL relations in the optical and near-infrared bands in each of the three galaxies. Results. Our distance analysis of 31 SMC Cepheids with periods of 4–69 days yields tight PL relations in all studied bands, with slopes consistent with the corresponding LMC and MW relations. Adopting the very accurately determined LMC slopes for the optical and near-infrared bands, we determine the zero point offsets between the corresponding absolute PL relations in the three galaxies. Conclusions. We find that in all bands the metal-poor SMC Cepheids are intrinsically fainter than their more metal-rich counterparts in the LMC and MW. In the K band the metallicity effect is −0.23 ± 0.06 mag dex−1, while in the V, (V − I) Wesenheit index it is slightly stronger, −0.34 ± 0.06 mag dex−1. We find suggestive evidence that the metallicity sensitivity of the PL relation might be nonlinear, being small in the range between solar and LMC Cepheid metallicity, and becoming steeper towards the lower-metallicity regime.

scholarly journals Reclassification of Cepheids in the Gaia Data Release 2

2019 ◽  
Vol 625 ◽  
pp. A14 ◽  
Author(s):  
V. Ripepi ◽  
R. Molinaro ◽  
I. Musella ◽  
M. Marconi ◽  
S. Leccia ◽  
...  
Keyword(s):  
Zero Point ◽  
Type Ii ◽  
Classical Cepheids ◽  
Data Release ◽  
Extragalactic Distance Scale ◽  
First Time ◽  
Distance Indicators ◽  
Zero Points

Context. Classical Cepheids are the most important primary indicators for the extragalactic distance scale. Establishing the precise zero points of their period-luminosity and period-Wesenheit (PL/PW) relations has profound consequences on the estimate of H0. Type II Cepheids are also important distance indicators and tracers of old stellar populations. Aims. The recent Data Release 2 (DR2) of the Gaia spacecraft includes photometry and parallaxes for thousands of classical and Type II Cepheids. We seek to review the classification of Gaia DR2 Cepheids and to derive precise PL/PW for the Magellanic Clouds (MCs) and Galactic Cepheids. Methods. We adopted information from the literature and the Gaia astrometry and photometry to assign DR2 Galactic Cepheids to the classical, anomalous, and Type II Cepheids classes. Results. We reclassified the DR2 Galactic Cepheids and derived new precise PL/PW relations in the Gaia passbands for the MCs and Milky Way Cepheids. We investigated for the first time the dependence on metallicity of the PW relation for classical Cepheids in the Gaia bands, finding inconclusive results. Conclusions. According to our analysis, the zero point of the Gaia DR2 parallaxes as estimated from classical and Type II Cepheids seems likely to be underestimated by ∼0.07 mas, which agrees with recent literature. The next Gaia data releases are expected to fix this zero point offset to allow eventually a determination of H0 to less than 1%.

scholarly journals The Milky Way Cepheid Leavitt law based on Gaia DR2 parallaxes of companion stars and host open cluster populations

2020 ◽  
Vol 643 ◽  
pp. A115 ◽  
Author(s):  
Louise Breuval ◽  
Pierre Kervella ◽  
Richard I. Anderson ◽  
Adam G. Riess ◽  
Frédéric Arenou ◽  
...  
Keyword(s):  
Milky Way ◽  
Open Cluster ◽  
Hubble Constant ◽  
Zero Point ◽  
Spatially Resolved ◽  
Trigonometric Parallax ◽  
Novel Approach ◽  
Classical Cepheids ◽  
Average Cluster ◽  
Gaia Dr2

Aims. Classical Cepheids provide the foundation for the empirical extragalactic distance ladder. Milky Way Cepheids are the only stars in this class accessible to trigonometric parallax measurements. However, the parallaxes of Cepheids from the second Gaia data release (GDR2) are affected by systematics because of the absence of chromaticity correction, and occasionally by saturation. Methods. As a proxy for the parallaxes of 36 Galactic Cepheids, we adopt either the GDR2 parallaxes of their spatially resolved companions or the GDR2 parallax of their host open cluster. This novel approach allows us to bypass the systematics on the GDR2 Cepheids parallaxes that is induced by saturation and variability. We adopt a GDR2 parallax zero-point (ZP) of −0.046 mas with an uncertainty of 0.015 mas that covers most of the recent estimates. Results. We present new Galactic calibrations of the Leavitt law in the V, J, H, KS, and Wesenheit WH bands. We compare our results with previous calibrations based on non-Gaia measurements and compute a revised value for the Hubble constant anchored to Milky Way Cepheids. Conclusions. From an initial Hubble constant of 76.18 ± 2.37 km s−1 Mpc−1 based on parallax measurements without Gaia, we derive a revised value by adopting companion and average cluster parallaxes in place of direct Cepheid parallaxes, and we find H0 = 72.8 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 when all Cepheids are considered and H0 = 73.0 ± 1.9 (statistical + systematics) ±1.9 (ZP) km s−1 Mpc−1 for fundamental mode pulsators only.

scholarly journals Period–luminosity–metallicity relation of classical Cepheids

2020 ◽  
Vol 642 ◽  
pp. A230
Author(s):  
V. Ripepi ◽  
G. Catanzaro ◽  
R. Molinaro ◽  
M. Marconi ◽  
G. Clementini ◽  
...  
Keyword(s):  
Near Infrared ◽  
Data Gathering ◽  
Hubble Constant ◽  
Zero Point ◽  
Total Sample ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Point Of View ◽  
Classical Cepheids ◽  
Metal Abundance

Context. Classical Cepheids (DCEPs) are the most important primary indicators for the extragalactic distance scale. Establishing the dependence on metallicity of their period–luminosity and period–Wesenheit (PL and PW) relations has deep consequences for the estimate of the Hubble constant (H0). Aims. We investigate the dependence on metal abundance ([Fe/H]) of the PL and PW relations for Galactic DCEPs. Methods. We combined proprietary and literature photometric and spectroscopic data, gathering a total sample of 413 Galactic DCEPs (372 fundamental mode, DCEP_F, and 41 first-overtone, DCEP_1O) and constructed new metallicity-dependent PL and PW relations in the near-infrared adopting the astrometry-based luminosity. Results. We find indications that the slopes of the PL(KS) and PW(J, KS) relations for Galactic DCEPs might depend on metallicity on the basis of the comparison with the Large Magellanic Cloud relationships. Therefore we used a generalized form of the PL and PW relations to simultaneously take the metallicity dependence of the slope and intercept of these relations into account. Conclusions. We calculated PL and PW relations that for the first time explicitly include a metallicity dependence of the slope and intercept terms. The quality of the available data is insufficient, however, and we cannot yet present conclusive results, but they are relevant from a methodological point of view. The new relations are linked to the geometric measurement of the distance to the Large Magellanic Cloud and allowed us to estimate a Gaia DR2 parallax zero-point offset Δϖ = 0.0615 ± 0.004 mas from the dataset of DCEPs used in this work.

scholarly journals Three open clusters containing Cepheids: NGC 6649, NGC 6664, and Berkeley 55

2020 ◽  
Vol 644 ◽  
pp. A136
Author(s):  
J. Alonso-Santiago ◽  
I. Negueruela ◽  
A. Marco ◽  
H. M. Tabernero ◽  
N. Castro
Keyword(s):  
Stellar Evolution ◽  
Hubble Constant ◽  
Open Clusters ◽  
Galactic Rotation ◽  
Chemical Abundances ◽  
Peculiar Velocity ◽  
Classical Cepheids ◽  
The Mean ◽  
First Time ◽  
Age Estimates

Classical Cepheids in open clusters play an important role in benchmarking stellar evolution models, in addition to anchoring the cosmic distance scale and invariably securing the Hubble constant. Three pertinent clusters hosting classical Cepheids and red (super)giants are: NGC 6649, NGC 6664, and Berkeley 55. These clusters form the basis of analysis to assess newly acquired spectra (≈50), archival photometry, and Gaia DR2 data. Importantly, for the first time chemical abundances were determined for the evolved members of NGC 6649 and NGC 6664. We find that they are slightly metal-poor relative to the mean Galactic gradient. Also, an overabundance of Ba is observed. These two clusters likely belong to the thin disc and the latter finding supports the “s-enhanced” scenario of D’Orazi et al. (2009). NGC 6664 and Berkeley 55 exhibit radial velocities consistent with Galactic rotation, while NGC 6649 displays a peculiar velocity. The resulting age estimates for the clusters (≈70 Ma) imply masses of ≈6 M⊙ for the (super)giant demographic. Lastly, the observed yellow-to-red (super)giant ratio is lower than expected and the overall differences that are relative to the models reflect the outstanding theoretical uncertainties.

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.

scholarly journals TheHubble Space TelescopeKey Project on the Extragalactic Distance Scale. XXVI. The Calibration of Population II Secondary Distance Indicators and the Value of the Hubble Constant

2000 ◽  
Vol 529 (2) ◽  
pp. 745-767 ◽  
Author(s):  
Laura Ferrarese ◽  
Jeremy R. Mould ◽  
Robert C. Kennicutt, Jr. ◽  
John Huchra ◽  
Holland C. Ford ◽  
...  
Keyword(s):  
Hubble Constant ◽  
Distance Scale ◽  
Extragalactic Distance Scale ◽  
Distance Indicators

scholarly journals Separation between RR Lyrae and type II Cepheids and their importance for a distance determination: the case of omega Cen

2020 ◽  
Vol 644 ◽  
pp. A95 ◽  
Author(s):  
V. F. Braga ◽  
G. Bono ◽  
G. Fiorentino ◽  
P. B. Stetson ◽  
M. Dall’Ora ◽  
...  
Keyword(s):  
Near Infrared ◽  
Variable Stars ◽  
Evolutionary Stage ◽  
Distance Modulus ◽  
Type Ii ◽  
Fourier Decomposition ◽  
Rr Lyrae ◽  
Classical Cepheids ◽  
Extragalactic Distance Scale ◽  
Distance Indicators

The separation between RR Lyrae (RRLs) and type II Cepheid (T2Cs) variables based on their period is debated. Both types of variable stars are distance indicators, and we aim to promote the use of T2Cs as distance indicators in synergy with RRLs. We adopted new and existing optical and near-infrared (NIR) photometry of ω Cen to investigate several diagnostics (color-magnitude diagram, Bailey diagram, Fourier decomposition of the light curve, and amplitude ratios) for their empirical separation. We found that the classical period threshold at one day is not universal and does not dictate the evolutionary stage: V92 has a period of 1.3 days but is likely to be still in its core helium-burning phase, which is typical of RRLs. We also derived NIR period-luminosity relations and found a distance modulus of 13.65 ± 0.07 (err.) ± 0.01 (σ) mag, in agreement with the recent literature. We also found that RRLs and T2Cs obey the same period-luminosity relations in the NIR. This equivalence provides the opportunity of adopting RRLs+T2Cs as an alternative to classical Cepheids to calibrate the extragalactic distance scale.

scholarly journals MEASURING THE HUBBLE CONSTANT WITH THE HUBBLE SPACE TELESCOPE

2009 ◽  
Vol 5 (H15) ◽  
pp. 1-16 ◽  
Author(s):  
W. L. Freedman ◽  
R. C. Kennicutt ◽  
J. R. Mould
Keyword(s):  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Distance Scale ◽  
Space Telescope ◽  
Peculiar Velocities ◽  
Extragalactic Distance Scale ◽  
Distance Indicators

AbstractTen years ago our team completed the Hubble Space Telescope Key Project on the extragalactic distance scale. Cepheids were detected in some 25 galaxies and used to calibrate four secondary distance indicators that reach out into the expansion field beyond the noise of galaxy peculiar velocities. The result was H0 = 72 ± 8 km s−1 Mpc−1 and put an end to galaxy distances uncertain by a factor of two. This work has been awarded the Gruber Prize in Cosmology for 2009.

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