We present homogeneous and accurate iron abundances for 42 Galactic Cepheids based on high resolution (R ~ 38 000) high signal-to-noise ratio (S/N ≥ 100) optical spectra collected with UVES at VLT ...(128 spectra). The above abundances were complemented with high-quality iron abundances provided either by our group (86) or available in the literature. We were careful to derive a common metallicity scale and ended up with a sample of 450 Cepheids. We also estimated accurate individual distances for the entire sample by using homogeneous near-infrared photometry and the reddening free period-Wesenheit relations. The new metallicity gradient is linear over a broad range of Galactocentric distances (RG ~ 5–19 kpc) and agrees quite well with similar estimates available in the literature (–0.060 ± 0.002 dex/kpc). We also uncover evidence that suggests that the residuals of the metallicity gradient are tightly correlated with candidate Cepheid groups (CGs). The candidate CGs have been identified as spatial overdensities of Cepheids located across the thin disk. They account for a significant fraction of the residual fluctuations, and also for the large intrinsic dispersion of the metallicity gradient. We performed a detailed comparison with metallicity gradients based on different tracers: OB stars and open clusters. We found very similar metallicity gradients for ages younger than 3 Gyr, while for older ages we found a shallower slope and an increase in the intrinsic spread. The above findings rely on homogeneous age, metallicity, and distance scales. Finally, by using a large sample of Galactic and Magellanic Cepheids for which accurate iron abundances are available, we found that the dependence of the luminosity amplitude on metallicity is vanishing.
High-precision (
) new JHK observations of 226 of the brightest and nearest red clump stars in the solar neighbourhood are used to determine distance moduli for the Large Magellanic Cloud (LMC). The ...resulting K- and H-band values of 18.47 ± 0.02 and 18.49 ± 0.06 imply that any correction to the K-band Cepheid PL relation due to metallicity differences between Cepheids in the LMC and the solar neighbourhood must be quite small.
Context. The Cepheid period-luminosity (PL) relation is unquestionably one of the most powerful tools at our disposal for determining the extragalactic distance scale. While significant progress has ...been made in the past few years towards its understanding and characterization both on the observational and theoretical sides, the debate on the influence that chemical composition may have on the PL relation is still unsettled. Aims. With the aim to assess the influence of the stellar iron content on the PL relation in the V and K bands, we have related the V-band and the K-band residuals from the standard PL relations of Freedman et al. (2001, ApJ, 553, 47) and Persson et al. (2004, AJ, 128, 2239), respectively, to Fe/H. Methods. We used direct measurements of the iron abundances of 68 Galactic and Magellanic Cepheids from FEROS and UVES high-resolution and high signal-to-noise spectra. Results. We find a mean iron abundance (Fe/H) about solar (\sigma = 0.10) for our Galactic sample (32 stars), similar to -0.33 dex (\sigma = 0.13) for the Large Magellanic Cloud (LMC) sample (22 stars) and similar to -0.75 dex (\sigma = 0.08) for the Small Magellanic Cloud (SMC) sample (14 stars). Our abundance measurements of the Magellanic Cepheids double the number of stars studied up to now at high resolution. The metallicity affects the V- band Cepheid PL relation and metal-rich Cepheids appear to be systematically fainter than metal-poor ones. These findings depend neither on the adopted distance scale for Galactic Cepheids nor on the adopted LMC distance modulus. Current data do not allow us to reach a firm conclusion concerning the metallicity dependence of the K-band PL relation. The new Galactic distances indicate a small effect, whereas the old ones support a marginal effect. Conclusions. Recent robust estimates of the LMC distance and current results indicate that the Cepheid PL relation is not Universal.
We present homogeneous and accurate iron abundances for almost four dozen (47) of Galactic Cepheids using high-spectral resolution (R ~ 40 000) high signal-to-noise ratio (S/N ≥ 100) optical spectra ...collected with UVES at VLT. A significant fraction of the sample (32) is located in the inner disk (RG ≤ 6.9 kpc) and for half of them we provide new iron abundances. Current findings indicate a steady increase in iron abundance when approaching the innermost regions of the thin disk. The metallicity is super-solar and ranges from 0.2 dex for RG ~ 6.5 kpc to 0.4 dex for RG ~ 5.5 kpc. Moreover, we do not find evidence of correlation between iron abundance and distance from the Galactic plane. We collected similar data available in the literature and ended up with a sample of 420 Cepheids. Current data suggest that the mean metallicity and the metallicity dispersion in the four quadrants of the Galactic disk attain similar values. The first-second quadrants show a more extended metal-poor tail, while the third-fourth quadrants show a more extended metal-rich tail, but the bulk of the sample is at solar iron abundance. Finally, we found a significant difference between the iron abundance of Cepheids located close to the edge of the inner disk (Fe/H ~ 0.4) and young stars located either along the Galactic bar or in the nuclear bulge (Fe/H ~ 0). Thus suggesting that the above regions have had different chemical enrichment histories. The same outcome applies to the metallicity gradient of the Galactic bulge, since mounting empirical evidence indicates that the mean metallicity increases when moving from the outer to the inner bulge regions.
Abstract
We present photometric and high-dispersion spectroscopic measurements that show HR 7920 is a periodic variable. The photometry reveals at least four frequencies higher that 10 d−1, two of ...which are also probably present in the radial velocity variations. The frequencies are in a range typical of δ Scuti star pulsations. A further low frequency of about 2.8 d−1 may be present in both radial velocities and photometry; if real, this points to γ Doradus variability, which would make HR 7920 a hybrid pulsator. An attempt is made to identify the modes of the δ Scuti pulsations, which include both radial and non-radial modes. A new rotational velocity of 75 km s−1 is derived from co-added spectra, contrasting with published values in the range 128–150 km s−1.
ABSTRACT
Multiwavelength variability studies of active galactic nuclei can be used to probe their inner regions that are not directly resolvable. Dust reverberation mapping (DRM) estimates the size ...of the dust emitting region by measuring the delays between the infrared (IR) response to variability in the optical light curves. We measure DRM lags of Zw229-015 between optical ground-based and Kepler light curves and concurrent IR Spitzer 3.6 and 4.5 µm light curves from 2010 to 2015, finding an overall mean rest-frame lag of 18.3 ± 4.5 d. Each combination of optical and IR light curve returns lags that are consistent with each other within 1σ, which implies that the different wavelengths are dominated by the same hot dust emission. The lags measured for Zw229-015 are found to be consistently smaller than predictions using the lag–luminosity relationship. Also, the overall IR response to the optical emission actually depends on the geometry and structure of the dust emitting region as well, so we use Markov chain Monte Carlo modelling to simulate the dust distribution to further estimate these structural and geometrical properties. We find that a large increase in flux between the 2011–2012 observation seasons, which is more dramatic in the IR light curve, is not well simulated by a single dust component. When excluding this increase in flux, the modelling consistently suggests that the dust is distributed in an extended flat disc, and finds a mean inclination angle of 49$^{+3}_{-13}$ deg.
The EBLM project Chew, Y Gomez Maqueo; Morales, J C; Faedi, F ...
Astronomy and astrophysics (Berlin),
12/2014, Letnik:
572
Journal Article, Publication
Recenzirano
Odprti dostop
In this paper, we derive the fundamental properties of 1SWASPJ011351.29+314909.7 (JO113+31), a metal-poor (-0.40 + or - 0.04 dex), eclipsing binary in an eccentric orbit (~0.3) with an orbital period ...of ~14.277 d. Eclipsing M dwarfs that orbit solar-type stars (EBLMs), like JO113+31, have been identified from their light curves and follow-up spectroscopy in the course of the WASP transiting planet search. We present the analysis of the first binary of the EBLM sample for which masses, radii and temperatures of both components are derived, and thus, define here the methodology. The primary component with a mass of 0.945 + or - 0.045 M sub(middot in circle) has a large radius (1.378 + or - 0.058 R sub(middot in circle)) indicating that the system is quite old, ~9.5 Gyr. The M-dwarf secondary mass of 0.186 + or - 0.010 M sub(middot in circle) and radius of 0.209 + or - 0.011 R sub(middot in circle) are fully consistent with stellar evolutionary models. However, from the near-infrared secondary eclipse light curve, the M dwarf is found to have an effective temperature of 3922 + or - 42 K, which is ~600 K hotter than predicted by theoretical models. We discuss different scenarios to explain this temperature discrepancy. The case of J0113+31 for which we can measure mass, radius, temperature, and metallicity highlights the importance of deriving mass, radius, and temperature as a function of metallicity for M dwarfs to better understand the lowest mass stars. The EBLM Project will define the relationship between mass, radius, temperature, and metallicity for M dwarfs providing important empirical constraints at the bottom of the main sequence.
We present new absolute trigonometric parallaxes and proper motions for seven Population II variable stars--five RR Lyr variables: RZ Cep, XZ Cyg, SU Dra, RR Lyr, and UV Oct; and two type 2 Cepheids: ...VY Pyx and Delta *k Pav. We obtained these results with astrometric data from Fine Guidance Sensors, white-light interferometers on Hubble Space Telescope. We find absolute parallaxes in milliseconds of arc: RZ Cep, 2.12 ? 0.16 mas; XZ Cyg, 1.67 ? 0.17 mas; SU Dra, 1.42 ? 0.16 mas; RR Lyr, 3.77 ? 0.13 mas; UV Oct, 1.71 ? 0.10 mas; VY Pyx, 6.44 ? 0.23 mas; and Delta *k Pav, 5.57 ? 0.28 mas; an average Delta *s Delta *p/ Delta *p = 5.4%. With these parallaxes, we compute absolute magnitudes in V and K bandpasses corrected for interstellar extinction and Lutz-Kelker-Hanson bias. Using these RR Lyrae variable star absolute magnitudes, we then derive zero points for MV -Fe/H and MK -Fe/H-log P relations. The technique of reduced parallaxes corroborates these results. We employ our new results to determine distances and ages of several Galactic globular clusters and the distance of the Large Magellanic Cloud. The latter is close to that previously derived from Classical Cepheids uncorrected for any metallicity effect, indicating that any such effect is small. We also discuss the somewhat puzzling results obtained for our two type 2 Cepheids.
We present the largest near-infrared (NIR) data sets, JHKs, ever collected for classical Cepheids in the Magellanic Clouds (MCs). We selected fundamental (FU) and first overtone (FO) pulsators, and ...found 4150 (2571 FU, 1579 FO) Cepheids for Small Magellanic Cloud (SMC) and 3042 (1840 FU, 1202 FO) for Large Magellanic Cloud (LMC). Current sample is 2-3 times larger than any sample used in previous investigations with NIR photometry. These are consistent with recent results from pulsation models and observations suggesting that the PW relations are minimally affected by the metal content. The new EU and FO PW relations were calibrated using a sample of Galactic Cepheids with distances based on trigonometric parallaxes and Cepheid pulsation models. These new MC distances lead to the relative distance, Delta mu = 0.48 + or - 0.03 mag (FU, log P = 1) and Delta mu = 0.52 + or - 0.03 mag (FO, log P = 0.5), which agrees quite well with previous estimates based on robust distance indicators.
We gathered more than 1130 high-resolution optical spectra for more than 250 Galactic classical Cepheids. The spectra were collected with the optical spectrographs UVES at VLT, HARPS at 3.6 m, FEROS ...at 2.2 m MPG/ESO, and STELLA. To improve the effective temperature estimates, we present more than 150 new line depth ratio (LDR) calibrations that together with similar calibrations already available in the literature allowed us to cover a broad range in wavelength (5348 ≤ λ ≤ 8427 Å) and in effective temperature (3500 ≤ Teff ≤ 7700 K). This gives us the unique opportunity to cover both the hottest and coolest phases along the Cepheid pulsation cycle and to limit the intrinsic error on individual measurements at the level of ~100 K. As a consequence of the high signal-to-noise ratio of individual spectra, we identified and measured hundreds of neutral and ionized lines of heavy elements, and in turn, have the opportunity to trace the variation of both surface gravity and microturbulent velocity along the pulsation cycle. The accuracy of the physical parameters and the number of Fe I (more than one hundred) and Fe II (more than ten) lines measured allowed us to estimate mean iron abundances with a precision better than 0.1 dex. We focus on 14 calibrating Cepheids for which the current spectra cover either the entire or a significant portion of the pulsation cycle. The current estimates of the variation of the physical parameters along the pulsation cycle and of the iron abundances agree very well with similar estimates available in the literature. Independent homogeneous estimates of both physical parameters and metal abundances based on different approaches that can constrain possible systematics are highly encouraged.
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