Research Interests: Physics, Astrophysics, Astronomy, Interferometry, Stars, and 3 moreObservatory, Sky, and effective temperature
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Research Interests: Physics and Astrophysics
ABSTRACT
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ABSTRACT
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We present the largest near-infrared (NIR) data sets, JHKS, ever collected for classical Cepheids
Research Interests: Physics and Astrophysics
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The influence of chemical composition on the properties of
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Laney & Stobie (1995) (LS95) have determined Baade-Wesselink radii for 49 galactic Cepheids using BVRI and JHK photometry. Four of the possible magnitude-colour combinations were studied in detail — namely, (V,B–V), (V,V–Ic), (K,V–K) and... more
Laney & Stobie (1995) (LS95) have determined Baade-Wesselink radii for 49 galactic Cepheids using BVRI and JHK photometry. Four of the possible magnitude-colour combinations were studied in detail — namely, (V,B–V), (V,V–Ic), (K,V–K) and (K,J–K). In that paper and in the present note we have used the maximum likelihood method of Balona (1977) as recently modified to allow for the nonlinear effects of the non-negligible radius excursions of Cepheids.One major advantage of infrared photometry is that the light variation at K is dominated by the change in surface area, unlike the light variation at V which is dominated by temperature changes. Another is that (as shown both empirically and by model atmospheres) one may use a J–K or V–K colour index to calculate the surface brightness at K without having to worry very much about the effects of varying surface gravity or Doppler broadening velocity, while the same is definitely not true when optical colour indices are used to calculate th...
Research Interests: Physics and COLLOQUIUM
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Context. Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the period-luminosity relations that provide accurate distances and the large number of spectral lines, Cepheids... more
Context. Galactic abundance gradients set strong constraints to chemo-dynamical evolutionary models of the Milky Way. Given the period-luminosity relations that provide accurate distances and the large number of spectral lines, Cepheids are excellent tracers of the present-day abundance gradients. Aims. We want to measure the Galactic abundance gradient of several chemical elements. While the slope of the Cepheid iron gradient did not vary much from the very first studies, the gradients of the other elements are not that well constrained. In this paper we focus on the inner and outer regions of the Galactic thin disk. Methods. We use high-resolution spectra (FEROS, ESPADONS, NARVAL) to measure the abundances of several light (Na, Al), α (Mg, Si, S, Ca), and heavy elements (Y, Zr, La, Ce, Nd, Eu) in a sample of 65 Milky Way Cepheids. Combining these results with accurate distances from period-Wesenheit relations in the near-infrared enables us to determine the abundance gradients in ...
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For 51 galactic Cepheids an average of 31 JHK observations per star have been obtained, sufficiently well distributed in phase to permit Fourier fitting and the determination of mean magnitudes and colours whose accuracy (about ± 0.01... more
For 51 galactic Cepheids an average of 31 JHK observations per star have been obtained, sufficiently well distributed in phase to permit Fourier fitting and the determination of mean magnitudes and colours whose accuracy (about ± 0.01 mag) is primarily determined by the internal consistency of the standard system used (Carter 1990, MNRAS, 242). Limited L data have been obtained for 42 of these stars
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Presentation des observations photometriques et spectroscopiques de SN 1987A effectuees a l'Observatoire Sutherland du SAAO entre 386 et 616 jours apres l'episode de neutrinos de Kamiokande-II
We present new estimates of the relative distance of the Magellanic Clouds (MCs) by using NIR and Optical-NIR Cepheid Period Wesenheit (PW) relations. The relative distances are independent of uncertainties affecting the zero-point of the... more
We present new estimates of the relative distance of the Magellanic Clouds (MCs) by using NIR and Optical-NIR Cepheid Period Wesenheit (PW) relations. The relative distances are independent of uncertainties affecting the zero-point of the PW relations, but do depend on the adopted pivot periods. We estimated the pivot periods for fundamental (FU) and first overtone (FO) Cepheids on the basis of their period distributions. We found that log P=0.5 (FU) and log P=0.3 (FO) are solid choices, since they trace a main peak and a shoulder in LMC and SMC period distributions. By using the above pivot periods and ten PW relations, we found MC relative distances of 0.53$\pm$0.06 (FU) and 0.53$\pm$0.07 (FO) mag. Moreover, we investigated the possibility to use mixed-mode (FU/FO, FO/SO) Cepheids as distance indicators and we found that they follow quite well the PW relations defined by single mode MC Cepheids, with deviations typically smaller than 0.3{\sigma}.
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Abstract Infrared and optical absolute magnitudes are derived for the type II Cepheids kappa Pav and VY Pyx using revised Hipparcos parallaxes and for kappa Pav, V553 Cen and SW Tau from pulsational parallaxes. Revised Hipparcos and HST... more
Abstract Infrared and optical absolute magnitudes are derived for the type II Cepheids kappa Pav and VY Pyx using revised Hipparcos parallaxes and for kappa Pav, V553 Cen and SW Tau from pulsational parallaxes. Revised Hipparcos and HST parallaxes for RR Lyrae agree satisfactorily and are combined in deriving absolute magnitudes. Phase-corrected J, H and Ks mags are given for 142 Hipparcos RR Lyraes based on Two-Micron All-Sky Survey observations. Pulsation and trigonometrical parallaxes for classical Cepheids are ...
This paper presents spectroscopic and photometric observations of SN 1987a in the Large Magellanic Cloud, made at the Sutherland field station of SAAO and in Cape Town for days 51-134 after the Kamiokande-II neutrino event. During this... more
This paper presents spectroscopic and photometric observations of SN 1987a in the Large Magellanic Cloud, made at the Sutherland field station of SAAO and in Cape Town for days 51-134 after the Kamiokande-II neutrino event. During this period, both the bolometric flux from the supernova and the apparent angular radius of the photosphere reached a maximum and subsequently declined. Some
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Baade–Wesselink radii derived using VJHK photometry are used to test the metallicity dependence of the Cepheid P–L relation using three collections of metallicity estimates from the literature. The hypothesis that Cepheids at the LMC... more
Baade–Wesselink radii derived using VJHK photometry are used to test the metallicity dependence of the Cepheid P–L relation using three collections of metallicity estimates from the literature. The hypothesis that Cepheids at the LMC metallicity ([Fe/H] ~ −0.2) could be several tenths of a magnitude fainter than at solar metallicity is not supported by the evidence.
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The Hipparcos survey team discovered thousands of new variables, including M giants with periods as short as a day, which appear to have maintained rough phase coherence over a period of more than three years. New optical and infrared... more
The Hipparcos survey team discovered thousands of new variables, including M giants with periods as short as a day, which appear to have maintained rough phase coherence over a period of more than three years. New optical and infrared photometry has been obtained as part of an effort to understand the nature of these anomalous stars.
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Metal-poor Cepheids do not appear to have smaller radii or cooler temperatures than more metal-rich Cepheids. A correction to the LMC modulus of 0.4 mag, due to metal-poor Cepheids being fainter for their periods, is inconsistent with the... more
Metal-poor Cepheids do not appear to have smaller radii or cooler temperatures than more metal-rich Cepheids. A correction to the LMC modulus of 0.4 mag, due to metal-poor Cepheids being fainter for their periods, is inconsistent with the data at the 6σ level or greater.
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Accurate MK temperature and luminosity classes have been obtained for 58 Cepheids in the Galaxy and in the Magellanic Clouds from 121 spectrograms. Classification criteria for the spectral region 3700X–6000X in the spectra of F-K... more
Accurate MK temperature and luminosity classes have been obtained for 58 Cepheids in the Galaxy and in the Magellanic Clouds from 121 spectrograms. Classification criteria for the spectral region 3700X–6000X in the spectra of F-K supergiants are described. The spectra of galactic and LMC Cepheids are found to be similar, and Cepheids in both systems appear to obey the same relation between (B-V)o and spectral type. The low E(B-V) values of Parsons (1970) and certain other recent authors are confirmed. The spectra of SMC Cepheids show slightly weaker metal lines relative to galactic Cepheid spectra, and SMC Cepheids average about 1.3 subclasses earlier in spectral type than LMC and galactic Cepheids at the same value of (B-V)o. Reddenings for both Clouds are found to be less than 0.05. Among supergiants (Mv = −4 to −8), stars of the same spectral type have the same (B-V)o regardless of luminosity class. Spectral types at minimum light are found to be later than those reported by Feas...
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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... more
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 ...
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Baade-Wesselink radii for dwarf Cepheids (High Amplitude Delta Scuti stars) can give luminosities and distances independent of the classical Cepheid distance scale. Using optical and IR photometry together with precision radial... more
Baade-Wesselink radii for dwarf Cepheids (High Amplitude Delta Scuti stars) can give luminosities and distances independent of the classical Cepheid distance scale. Using optical and IR photometry together with precision radial velocities, the authors have obtained radii and luminosities for 7 stars, and combined these with two from the literature, obtaining results consistent with the luminosities of the 3 dwarf Cepheids with good Hipparcos parallaxes. Classical Cepheids and dwarf Cepheids appear to fit the same PL and PR relations. The results imply ‘bright’ RR Lyrae absolute magnitudes giving an LMC distance modulus of 18.51-18.54, in agreement with the distance derived from classical Cepheids.
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The paper presents spectroscopic and UBV(RI)cJHKLM photometric observations of SN1987A in the Large Magellanic Cloud made between days 617 and 792 after the Kamiokande-II neutrino e vent. During the period from day 520 to day 630 the U to... more
The paper presents spectroscopic and UBV(RI)cJHKLM photometric observations of SN1987A in the Large Magellanic Cloud made between days 617 and 792 after the Kamiokande-II neutrino e vent. During the period from day 520 to day 630 the U to M bolometric flux went through a very steep decline, returning after day 670 to the same decline rate as before day