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 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 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 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.

MACHINE LEARNING ALGORITHMS FOR IDENTIFICATION OF ABNORMAL GLOW CURVES AND ASSOCIATED ABNORMALITY IN CaSO4:DY-BASED PERSONNEL MONITORING DOSIMETERS

2020 ◽  
Vol 190 (3) ◽  
pp. 342-351
Author(s):  
Munir S Pathan ◽  
S M Pradhan ◽  
T Palani Selvam
Keyword(s):  
Machine Learning ◽  
Glow Curve ◽  
Good Accuracy ◽  
Machine Learning Algorithms ◽  
Support Vector ◽  
Computationally Efficient ◽  
Artificial Neural Network Ann ◽  
First Time

Abstract In the present study, machine learning (ML) methods for the identification of abnormal glow curves (GC) of CaSO4:Dy-based thermoluminescence dosimeters in individual monitoring are presented. The classifier algorithms, random forest (RF), artificial neural network (ANN) and support vector machine (SVM) are employed for identifying not only the abnormal glow curve but also the type of abnormality. For the first time, the simplest and computationally efficient algorithm based on RF is presented for GC classifications. About 4000 GCs are used for the training and validation of ML algorithms. The performance of all algorithms is compared by using various parameters. Results show a fairly good accuracy of 99.05% for the classification of GCs by RF algorithm. Whereas 96.7% and 96.1% accuracy is achieved using ANN and SVM, respectively. The RF-based classifier is recommended for GC classification as well as in assisting the fault determination of the TLD reader system.

On the morphology and classification of larval water mites (Hydrachnidia, Acari) from springs in Luxembourg

Zootaxa ◽  
2006 ◽  
Vol 1138 (1) ◽  
pp. 1 ◽  
Author(s):  
PETER MARTIN
Keyword(s):  
Morphological Data ◽  
Water Mites ◽  
Water Mite ◽  
Question Mark ◽  
First Time

Morphological data on the larvae of 37 species of freshwater mites (Hydrachnidia) known from springs in Luxembourg are reported. Larvae of Sperchon insignis (Walter, 1906), S. longissimus K.Viets, 1920, Lebertia holsatica K. Viets, 1920, Atractides fonticolus (K.Viets, 1920) and, with a question mark, A. pennatus (K.Viets, 1920) are described for the first time; re-descriptions are presented for Sperchon squamosus Kramer, 1879 and S. setiger Thor, 1898. Previous larval descriptions are listed and commented on for all species. Two species are recorded as new for the Luxembourgian fauna: Panisellus thienemanni (K.Viets, 1920) and Pseudofeltria scourfieldi Soar, 1904. A further taxon previously not recorded from springs in Luxembourg is described, probably Tiphys Koch, 1836 sp. An illustrated key is presented suitable for the determination of most parasitic water mite larvae attached to insect hosts from Luxembourgian springs.

scholarly journals The Cepheid period–luminosity–metallicity relation based on Gaia DR2 data

2018 ◽  
Vol 619 ◽  
pp. A8 ◽  
Author(s):  
M. A. T. Groenewegen
Keyword(s):  
Strong Correlation ◽  
Goodness Of Fit ◽  
Zero Point ◽  
Distance Scale ◽  
Distance Modulus ◽  
Initial Sample ◽  
Classical Cepheids ◽  
Data Release ◽  
Multi Mode ◽  
Gaia Dr2

Aims. We use parallax data from the Gaia second data release (GDR2), combined with parallax data based on HIPPARCOS and HST data, to derive the period–luminosity–metallicity (PLZ) relation for Galactic classical cepheids (CCs) in the V, K, and Wesenheit WVK bands. Methods. An initial sample of 452 CCs are extracted from the literature with spectroscopically derived iron abundances. Reddening values, classifications, pulsation periods, and mean V- and K-band magnitudes are taken from the literature. Based on nine CCs with a goodness-of-fit (GOF) statistic smaller than 8 and with an accurate non-Gaia parallax (σπ comparable to that in GDR2), a parallax zero-point offset of −0.049 ± 0.018 mas is derived. Selecting a GOF statistic smaller than 8 removes about 40% of the sample most likely related due to binarity. Excluding first overtone and multi-mode cepheids and applying some other criteria reduces the sample to about 200 stars. Results. The derived PL(Z) relations depend strongly on the parallax zero-point offset. The slope of the PL relation is found to be different from the relations in the LMC at the 3σ level. Fixing the slope to the value found in the LMC leads to a distance modulus (DM) to the LMC of order 18.7 mag, larger than the canonical distance. The canonical DM of around 18.5 mag would require a parallax zero-point offset of order −0.1 mas. Given the strong correlation between zero point, period and metallicity dependence of the PL relation, and the parallax zero-point offset there is no evidence for a metallicity term in the PLZ relation. Conclusions. The GDR2 release does not allow us to improve on the current distance scale based on CCs. The value of and the uncertainty on the parallax zero-point offset leads to uncertainties of order 0.15 mag on the distance scale. The parallax zero-point offset will need to be known at a level of 3 μas or better to have a 0.01 mag or smaller effect on the zero point of the PL relation and the DM to the LMC.

Distances of nearby Groups and Clusters, and the Local Value of the Hubble Ratio

1977 ◽  
Vol 37 ◽  
pp. 301-307
Author(s):  
G. de Vaucouleurs
Keyword(s):  
Globular Clusters ◽  
Zero Point ◽  
Rr Lyrae ◽  
Galactic Clusters ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
Absolute Magnitudes ◽  
Extragalactic Distance Scale ◽  
Zero Points ◽  
Local Value

AbstractThe correct approach to build up the extragalactic distance scale is to use all available primary (novae, cepheids, RR Lyrae) and secondary indicators (brightest stars, globular clusters, largest HII rings) to calibrate without arbitrary extrapolation all reliable tertiary indicators (magnitudes and diameters of galaxies), precisely corrected for all known effects of type, luminosity class, orientation, internal and galactic extinction and redshift. Such data are now available for over 1000 galaxies in the Second Reference Catalogue.Revised distances to members of the Local Group from primary indicators and new estimates of distances to the nearest groups from primary and secondary indicators are used to calibrate the tertiary indicators via a new, composite luminosity index.The distances derived from globular clusters for 3 galaxy clusters dominated by ellipticals (Vir I, For I, Hya I) with mean corrected velocities 1000 ≤ Vo ≤ 3650 km s-1 give a mean Hubble ratio <H> = 88 (1 ± 0.15) km s-1 Mpc-1. This value rests entirely on the calibration of the globular clusters luminosity function in the Galaxy as a gaussian of dispersion σ = 1.1 mag. and mean <MB>(⊕) = -6.55, with <(B-V)o > = 0.75, based on the adopted RR Lyrae zero point <Mv> (RR) = + 0.86 ± 0.15.The distances derived from tertiary indicators to 19 field spirals and 28 nearby groups dominated by spirals with corrected velocities Vo < 1800 km s-1 give <H> = 82 (1 ± 0.15) km s-1 Mpc-1. This value rests on the relations between luminosity index and fully corrected absolute magnitudes or linear diameters of galaxies derived without extrapolation and calibrated in ~20 nearby galaxies by seven secondary indicators. The zero points were derived from the 3 primary indicators, including 15 galactic novae with <M15> = -5.5 ± 0.15, and 13 cepheids in 8 galactic clusters with <MB> (logPo = 0.8) = -2.92 ± 0.15 (for an adopted Hyades modulus of 3.16 ± 0.05).The low values of Ho≃50 to 55 can be explained by an accumulation of complex systematic errors arising from a multiplicity of sources. These errors, all but one acting in the same sense, have been identified and evaluated; a full report will appear elsewhere.

scholarly journals Classification of Wolf-Rayet stars in NGC 595 in M 33 through high-spatial resolution observations

2003 ◽  
Vol 212 ◽  
pp. 572-573 ◽  
Author(s):  
Pierre Royer ◽  
Ingemar Lundström ◽  
Jean-Marie Vreux
Keyword(s):  
Stellar Population ◽  
Angular Resolution ◽  
High Angular Resolution ◽  
Photometric Technique ◽  
H Ii Region ◽  
The One ◽  
First Time ◽  
Rayet Star

NGC 595 is, after NGC 604, the second most luminous H ii region in the Milky Way's neighbouring spiral galaxy M 33. Its Wolf-Rayet star content has mainly been unveiled by two different channels. On the one hand, the stellar population of NGC 595 has been resolved and its WR stars identified through online/off-line H ii λ4686 observations realised with the HST. Nevertheless, due to the limited number of filters used, this did not give any information on the WR spectral subtypes. On the other hand, spectroscopic observations of NGC 595, realised at optical and ultraviolet wavelengths, have enabled the determination of some spectral subtypes, but this time, the lack of angular resolution did not allow to resolve the whole population. Thanks to our photometric technique, based on five dedicated narrow-band filters, we present here a determination of the spectral subtypes of NGC 595 WR stars which for the first time combines high-angular resolution and high-‘spectroscopic’ discrimination capabilities.

scholarly journals Classical Cepheids, what else?

2012 ◽  
Vol 8 (S289) ◽  
pp. 116-125 ◽  
Author(s):  
G. Bono ◽  
L. Inno ◽  
N. Matsunaga ◽  
K. Genovali ◽  
B. Lemasle ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Near Infrared ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Distance Modulus ◽  
Period Range ◽  
Classical Cepheids ◽  
Similar Distance ◽  
Distance Indicators ◽  
Zero Points

AbstractWe present new and independent estimates of the distances to the Magellanic Clouds (MCs) using near-infrared (NIR) and optical–NIR period–Wesenheit (PW) relations. The slopes of the PW relations are, within the dispersion, linear over the entire period range and independent of metal content. The absolute zero points were fixed using Galactic Cepheids with distances based on the infrared surface-brightness method. The true distance modulus we found for the Large Magellanic Cloud—(m − M)0 = 18.48 ± 0.01 ± 0.10 mag—and the Small Magellanic Cloud—(m − M)0 = 18.94 ± 0.01 ± 0.10 mag—agree quite well with similar distance determinations based on robust distance indicators. We also briefly discuss the evolutionary and pulsation properties of MC Cepheids.

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