LMC Cepheids Research Articles

The First Steps of the Extragalactic Distance Ladder

view Abstract Citations (12) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The First Steps of the Extragalactic Distance Ladder Bohm-Vitense, Erika Abstract Recent distance determinations by means of the Cepheid period-magnitude relations are based on a true distance modulus of m-M=18.5 to the Large Magellanic Cloud. It has further been assumed that for the LMC Cepheids the average E(B-V)=0.10 and that the ratio of interstellar extinction Av in the visual to E(B-V), i.e., Rv, is 3.1. In order to determine the distance to the LMC with its lower than solar metallicity, it is also assumed that the period-magnitude relation is independent of metallicity. Here we reexamine the different assumptions, i.e., the reddening and distance to the LMC and to the Galactic Cepheids. We also study the dependence of the period-magnitude relations for different heavy element abundances. In that process we rediscuss the distances to the LMC, to M31 and the Small Magellanic Cloud. Adopting the theoretical result, that the period-luminosity relation is independent of metallicity, we derive for the V and B bands the dependence of the period-magnitude relations on Z. The use of these relations changes the determination of the interstellar extinction for the three M3 1 fields, studied by Freedman and Madore, and yields very good agreement for the distance moduli of the three fields, namely m-M=24.59±0.02, or (m-M)M31-(m-M)LMC=6.09± 0.02, where the error limits refer only to the internal agreement for the three fields. We adopt a foreground reddening of E(B-V)=0.08 for M31 and estimate an average E(B-V)=0.18 for the LMC Cepheids. With a distance modulus to the Pleiades, m-M=5.57, we derive a distance modulus to the LMC of m-M=18. 11 andm-M=18.84±0.1 for the SMC. These error limits are only estimates. We also point out a way to get a rough estimate about large metallicity differences of Cepheids observed in external galaxies. Publication: The Astronomical Journal Pub Date: January 1997 DOI: 10.1086/118232 Bibcode: 1997AJ....113...13B Keywords: DISTANCE SCALE full text sources ADS | data products SIMBAD (7) NED (3)

Empirical Approach to Cepheid Period-Luminosity-Color and Period-Luminosity Relations by Surface Brightness

view Abstract Citations (16) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Empirical Approach to Cepheid Period-Luminosity-Color and Period-Luminosity Relations by Surface Brightness di Benedetto, G. P. Abstract Empirical period-luminosity-color and period-luminosity (PLC [V, B-V] and PL[V] relations according to Stefan's law are derived for Cepheid variables by applying thermal scales of nonvariable giant and supergiant stars established by modern observational interferometry. Intrinsic surface brightnesses are predicted by the apparent color index V - K as fiducial reference unbiased by metallicity and gravity effects, along with current optical absorption data. Linear radii are inferred from periods through the period-radius relation, assumed to be insensitive to abundance and brightness variations. The dependence of PLC and PL zero points to abundance effects is further investigated. I compare current Cepheid data from our metal- normal Galaxy (GAL) with those in the Magellanic Clouds (LMC and SMC) of poorer metal content. The major achievement is that the PL(V) relations are found to be severely biased by metallicity, whereas the PLC(V, B- V) relations turn out to be much less affected by abundances than previously expected. The new PLC and PL relations calibrated on fundamental quantities are compared with those from the classical zero-age main-sequence (ZAMS) fitting empirical approach. It is shown that all metal-normal equations lead to remarkably consistent luminosities of GAL Cepheids, to within +/- 0.05 mag (PL) and +/- 0.02 mag (PLC), whereas metal-poor LMC and SMC results appear to be significantly discrepant. It is emphasized that theoretical thermal scales applied for the derivation of ZAMS metal- corrected relations, either explicit or implicit, are mainly responsible for such observed discrepancies. The actual empirical approach appears to overcome most of the previous difficulties closely related to the poor knowledge of Cepheid thermal properties. Theoretical Cepheid thermal scales are critically reviewed. It is found that recent metal-normal color-brightness relations lead to results remarkably consistent with those from observational scales, whereas metal-poor predictions appear to be overestimated, at least for Cepheid periods log P (days) > 1 currently observed in extragalactic work. Theoretical PLC(V, B-V) and PL(V) relations revised according to unbiased conversion scales now support the above finding that PLC relations are less affected by metallicity than PL relations. This also enables the reconciliation of evolution, pulsation, and stellar atmosphere theories since the ratio of evolution to pulsation mass is found to be very close to 1 for all GAL, LMC, and SMC Cepheids. Because of the poorer metal content of the Magellanic Clouds, current PL( V) distance to the LMC and SMC are found to be underestimated, being referred to metal-normal GAL Cepheids as primary calibrators. Distance moduli through either infrared photometry (V, V - K) (pulsation parallaxes) or optical photometry (V, B- V) now become (m - M)_0_(LMC) = 18.64 +/- 0.02, (m - M)_0_(SMC) = 19.09 +/- 0.02. Publication: The Astrophysical Journal Pub Date: October 1995 DOI: 10.1086/176291 Bibcode: 1995ApJ...452..195D Keywords: GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: MAGELLANIC CLOUDS; STARS: ABUNDANCES; STARS: FUNDAMENTAL PARAMETERS; STARS: OSCILLATIONS; STARS: VARIABLES: CEPHEIDS full text sources ADS | data products SIMBAD (3) NED (2)

EROS: Short Period Cepheids in the Bar of the LMC

AbstractWe present Fourier analysis at 490 nm for 87 Cepheid light curves in the bar of the Large Magellanic Cloud. The photometry has been obtained through the EROS project whose main purpose is the search for baryonic dark matter in the Galactic halo. The very high quality of the photometry and the good phase coverage enable us to obtain accurate Fourier decomposition of the light curves. As a consequence we confirm that the so-called s-Cepheids are overtone pulsators and represent about 30 % of our sample, whereas the Classical Cepheids are fundamental pulsators. We have identified a number of features in plots of amplitude ratios and phase differences versus period. These features are usually related to resonances between different pulsation modes. If we accept that Fourier decomposition techniques applied to light curves yield positions for the centres of resonances, then it seems that resonances occur in LMC Cepheids at the same period as in Galactic Cepheids for fundamental pulsators, whereas they appear to be at shorter periods for overtone pulsators.

Near-infrared variant of the Barnes-Evans method for finding Cepheid distances calibrated with high-precision angular diameters

view Abstract Citations (55) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Variants of the Barnes-Evans Method for Finding Cepheid Distances Calibrated With High-Precision Angular Diameters Welch, Douglas L. Abstract The advantages of a near-infrared variant of the Barnes-Evans method for estimating distances to Cepheid variables are described and quantified. A surface brightness-color relation for $K$ photometry and the $(V-K)_0$ color index is established using modern, high-precision angular diameters from optical interferometers. Applied to data for the galactic (cluster) Cepheid U Sgr, this method yields a distance of 0.660 $\pm$ 0.024 kpc and a true distance modulus of 9.10 $\pm$ 0.07 mag. This estimate compares with the true distance modulus of 9.37 $\pm$ 0.22 mag estimated by Gieren, Barnes, and Moffett (1993) using the classical Barnes-Evans technique. The possibility of estimating distances of LMC and SMC Cepheids directly -- without intermediate steps -- is discussed. The feasibility of determining the distance of M31 or M33 using this technique is examined and is probably within the reach of 8m-class telescopes. Publication: The Astronomical Journal Pub Date: October 1994 DOI: 10.1086/117164 arXiv: arXiv:astro-ph/9407088 Bibcode: 1994AJ....108.1421W Keywords: Astrometry; Astronomical Interferometry; Astronomical Photometry; Brightness; Calibrating; Cepheid Variables; Diameters; Distance; Infrared Astronomy; Magellanic Clouds; Near Infrared Radiation; Absorption Spectra; Infrared Photometry; Stellar Color; Astronomy; STARS: DISTANCES; CEPHEIDS; STARS: FUNDAMENTAL PARAMETERS; Astrophysics E-Print: 19 pages + 3 figures, uuencoded compressed postscript, DLW-94-1 full text sources arXiv | ADS | data products SIMBAD (15)

The Hubble Space Telescope Extragalactic Distance Scale Key Project. 1: The discovery of Cepheids and a new distance to M81

We report on the discovery of 30 new Cepheids in the nearby galaxy M81 based on observations using the Hubble Space Telescope (HST). The periods of these Cepheids lie in the range of 10-55 days, based on 18 independent epochs using the HST wide-band F555W filter. The HST F555W and F785LP data have been transformed to the Cousins standard V and I magnitude system using a ground-based calibration. Apparent period-luminosity relations at V and I were constructed, from which apparent distance moduli were measured with respect to assumed values of mu(sub 0) = 18.50 mag and E(B - V) = 0.10 mag for the Large Magellanic Cloud. The difference in the apparent V and I moduli yields a measure of the difference in the total mean extinction between the M81 and the LMC Cepheid samples. A low total mean extinction to the M81 sample of E(B - V) = 0.03 +/- 0.05 mag is obtained. The true distance modulus to M81 is determined to be 27.80 +/- 0.20 mag, corresponding to a distance of 3.63 +/- 0.34 Mpc. These data illustrate that with an optimal (power-law) sampling strategy, the HST provides a powerful tool for the discovery of extragalactic Cepheids and their application to the distance scale. M81 is the first calibrating galaxy in the target sample of the HST Key Project on the Extragalactic Distance Scale, the ultimate aim of which is to provide a value of the Hubble constant to 10% accuracy.

Surface brightness distance determinations to the Large Magellanic Cloud Cepheid variables HV 899 and 2257*

We present new VRI light curves for the long-period LMC Cepheids HV899 and 2257 and combine these data with the CORAVEL radial velocity curves of Imbert to derive the distances to these variables using the surface brightness method. Assuming metallicities of [Fe/H]=(−0.4±0.2) for both supergiants, we find metallicity-corrected distances of (65.2±4.3) kpc for HV899 and (65.7±4.3) kpc for HV2257, which correspond to true distance moduli of (19.07±0.15) and (19.09±0.15) mag, respectively. These distance moduli are about 0.4 mag larger than those predicted for the LMC by the galactic Cepheid calibration of the surface brightness method of Gieren, Barnes & Moffett [which predicts μ 0 (LMC)∼18.65 mag]

Cepheids in Magellanic Cloud Clusters

AbstractThe Magellanic Clouds remain an ideal place to study the properties of Cepheid variables. In this paper, we review historical and current work on Cepheids in LMC and SMC clusters, present new results for NGC 1866 and NGC 2164, and describe a new technique for automated selection of Cepheid variables using two-color photometry. We also emphasize the numerous advantages of high-precision radial velocities in the study of Magellanic Cloud variables.

Cepheids in IC 4182, Calibration of SNIa 1937C and the Hubble constant

AbstractObservations with the Wide Field Camera on HST were examined, and 27 Cepheids were discovered. Photometry and period analysis have produced unambiguous light curves free of alias. The observed P-L relation has a slope consistent with seminal calibration studies of Galactic and LMC Cepheids. An apparent distance modulus (in V) of 28.47 ± 0.10 to IC 4182 is derived. This implies that Mv(max) for SNIa 1937C is -19.92 ± 0.2 mag, independent of everything except differential absorption between the Cepheids and the supernova. Using this to calibrate Hubble diagrams for SNIa by several authors, and allowing for a 1-σ uncertainty in the absolute magnitude from the calibration of only one SNIa, we obtain H0 = 45 ± 14kms-1Mpc-1.

A Preliminary Distance to the Small Magellanic Cloud by the Surface Brightness Technique

AbstractWe present a new distance determination to the Small Magellanic Cloud from the surface brightness technique applied to the Cepheid variable HV 829. Although this is a preliminary distance based on only one star, it illustrates the power of the surface brightness technique to extragalactic Cepheid distances, it develops the technique which we will apply to additional SMC and LMC Cepheids, and the distance is of intrinsic interest because of the current controvery concerning distances for the Magellanic Clouds.For HV 829 itself we obtain a distance modulus of 18.91 ± 0.20 mag. From other evidence we infer that HV 829 is slightly in front of the SMC centroid distance. Correcting to the SMC centroid yields a distance to the SMC of 19.05 ± 0.20 mag. We stress that this distance modulus is fully independent of any other distance modulus for the SMC, including those based upon Cepheids. Even so, our result agrees more closely with other, independent Cepheid distances than with RR Lyrae distances and main sequence fitting distances.

TUNING THE CEPHEID DISTANCE SCALE

ABSTRACT With the advent of a number of promising new secondary extragalactic distance indicators, the reliaable calibration of the Cepheid distance scale becomes increasingly imperative. Ongoing observational programs (both from the ground and space) promise to provide a significantly larger sample of galaxies with well-studied Cepheids both within the Local Group and in more distant galaxies. In this review I describe recent efforts in the calibration of the Cepheid distance scale using Cepheids in star clusters in the Galaxy and in the Magellanic Clouds. I emphasize some of the important advantages of using LMC Cepheids in particular, and summarize the current status of the field. Some of the complications involved in the methods discussed to calibrate the Cepheid distance scale are also described along with suggestions for future work.

New Cepheid distances to nearby galaxies based on BVRI CCD photometry. II - The local group galaxy M33

A true distance modulus to the nearby spiral galaxy M33 has been determined based on CCD photometry obtained at BVRI wavelengths. M33 is presently one of five nearby galaxies used in the calibration of the IR Tully-Fisher relation, and thereby in the determination of the Hubble constant. Using period-luminosity relations at several wavelengths offers the advantage that the distance moduli derived can be corrected for the effects of interstellar extinction. These data indicate that there is internal reddening affecting the Cepheid photometry in M33 which must be accounted for if a true distance modulus is to be obtained for this galaxy. Adopting a true distance modulus to the LMC of 18.5 mag, the new CCD data yield a true distance to M33 of 24.64 + or - 0.09 mag, corresponding to a linear distance of 840 kpc. A mean value of the total color excess (foreground and internal) for the Cepheids in M33 is estimated to be E(B - V) = 0.10 + or - 0.09 mag, assuming a value for the total mean LMC Cepheid color excess of 0.10 mag.

Infrared Observations of Galactic Cepheids

AbstractInfrared photometry enables radii, and hence absolute magnitudes, to be derived more accurately than is possible using purely optical photometry. In this paper we present BVJHK observations of the galactic cepheids T Vul, U Vul and T Mon. Using this data we find reasonable agreement with current versions of the Period-Luminosity relations, in both the optical and infrared.From these relations and existing optical and infrared data for LMC Cepheids we find for the LMC (i) Av = 0.35 and (ii) a distance modulus of 18.50. In addition we show that the P-L-C relation has the form<Mv> = – 3.10 log P + 1.70 (<B>–<V>) – 2.37

Spectral Types, Color Indices, and Abundances for Cepheids in the Magellanic Clouds and the Galaxy

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 Feast (1974) when luminosity effects are allowed for. Spectroscopic surface gravities near minimum light appear to be lower than those near maximum and slightly fainter Mv values are found at each luminosity class than those usually cited. SMC Cepheids appear to have lower surface gravities than LMC Cepheids at the same absolute magnitude, as one would expect from the lower metal abundances.

Period Changes in Magellanic Cloud Cepheids

It has been found possible to obtain information on period change in data on 115 cepheid variable stars in the Magellanic Clouds (84 LMC cepheids and 31 SMC cepheids). Harvard Observatory data of the period 1910 to 1950 (collated by Payne-Gaposchkin and Gaposchkin) are combined with Dunsink Observatory observations carried out by C.J. Butler in 1966/67 and with South African Astronomical Observatory observations covering the years 1975–1977 by Martin, Thomas, Carter and Davies to derive mean periods for the intervals between the various data sets. Using these new periods in conjunction with the very accurate Harvard periods, seperate estimates of the time averaged fractional change of period per day, d/dt (ln P), with corresponding estimated errors, could be evaluated for two epochs, one around 1950 and the other around 1971. It was found that 70 stars give rates of change of period that are not significantly different from zero, that 20 stars have two values of rate of change of period that are in agreement at the two epochs (indicative of secular period change), while 22 stars give two disparate values of rate of change of period (indicative of irregular period changes).

Period-luminosities relation of classical Cepheids

A new PL-relation (10) — Figure 2 for the Cepheids in the Galaxy, the Magellanic Clouds and M31 has been constructed. On deriving this relation both the period-radius (3) and period-colour relations (7), (8) and (9) are essentially used. The PC-relation (7) determined after the colours of 88 galactic cepheids (Table I), which are obtained from the colour-spectrum relation (6) — Figure 1, common for Cepheids and non-variable supergiants, are used also for the M31 Cepheids, whereas (8) and (9) are for the Large and Small MC Cepheids, respectively, all three PC-relations having a common slope. The comparison of the relations (8) and (9) with (7) shows that the LMC and SMC Cepheids are bluer than the galactic ones with 0m.04 and 0m.19, respectively, probably because of their metal-poor abundance.

Photometry of Cepheids in the LMC and Magellanic Cloud abundances

view Abstract Citations (35) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Photometry of Cepheids in the LMC and Magellanic Cloud abundances Harris, H. C. Abstract Washington-system colors of 40 Cepheids in the Large Magellanic Cloud are used to study the metal abundances within the LMC and to compare with abundances in the SMC and the Galaxy. The LMC Cepheids are quite homogeneous: they show a dispersion in observed [A/H] of ±0.14, probably due to a width for the instability strip of about 0m.07 in T1 - T2 (about 400 K) combined with a real dispersion in [A/H] of ±0.1. Neither they nor SMC Cepheids show the correlation of residuals from the P - L relation with abundance which has been predicted based on evolutionary models. The values of reddening found within the LMC are weakly correlated with H I column density, and are sufficiently small [mean E (T1 - T2) = 0m.04] that the derived dust/gas ratio in the LMC is 0.4 times that in the Galaxy. No gradient in abundances within the LMC is found, either with east-west position or radially. It is suggested that variations both in the B/R ratio of supergiants and in the mean periods of Cepheids across the LMC might be better explained by variations in the rate of star formation rather than by abundance variations. The abundances of the LMC and SMC Cepheids relative to Galactic Cepheids are found to be -0.09 and -0.65, respectively, and are compared with results from other studies. Publication: The Astronomical Journal Pub Date: April 1983 DOI: 10.1086/113336 Bibcode: 1983AJ.....88..507H Keywords: Astronomical Photometry; Cepheid Variables; Magellanic Clouds; Metallicity; Interstellar Extinction; Luminosity; Milky Way Galaxy; Stellar Color; Stellar Magnitude; Astrophysics full text sources ADS | data products SIMBAD (38) NED (1) GCPD (1)

On the determination of the colour term in the P–L–C relation for cepheids

The recent speculations by Brodie & Madore and by Qube & Dawe that the coefficient of the colour term in the P–L–C relation for cepheids may be considerably different from 2.7 are inconsistent with existing data on LMC cepheids. The colour coefficient recently derived by Martin, Warren & Feast is not significantly affected by taking into account an absorption induced correlation between the errors in |$\langle V_0\rangle$| and |$(\langle B_0\rangle-\langle V_0\rangle)$|⁠. The computer simulation of Brodie & Madore which shows the bias introduced in the colour coefficient when this is derived by an inappropriate method (simple least squares) is consistent with theory and in accord with actual results in the LMC. This gives added confidence in the unbiased nature of the results of Martin, Warren & Feast derived by a maximum likelihood method which takes into account errors in each variable.

Multicolour Photoelectric Photometry of Magellanic Cloud Cepheids

AbstractPhotoelectric B, V, I observations of LMC cepheids made at SAAO are combined with previous photoelectric B, V values and analysed. It is shown that a P-L-C relation gives a much better fit to the data that a P-L relation at least in the period range 0.9 < logP < 1.7. Individual corrections for interstellar reddening, are derived from the B, V, I results. The colour term in the P-L-C relation is shown to be intrinsic rather than due to differential interstellar reddening. We find,

Working Group on the Magellanic Clouds

A Symposium on the Magellanic Clouds was sponsored by E.S.O. in Santiago, Chile, in 1969 March in connection with the dedication of the E.S.O. Observatory at La Silla. Review papers on the Clouds have been written by Westerlund and Bok (J. R. astr. Soc. Can., 63, 105).Gascoigne (Mon. Not. R. astr. Soc., 146, 1) has prosecuted further his P-L work on Cloud cepheids and finds V = 17·58 — 3·072 logP (7 LMC cepheids), V = 17·73 — 2·879 logP (13 SMC cepheids) while 25 SMC, 18 LMC and 13 galactic cepheids obey the Sandage relation Mv = a – 3·609 logP + 2·52(<B> – <V>).This implies moduli of 18·73 (LMC) and 19·36 (SMC), but Gascoigne recommends, in the light of other evidence, adoption of moduli 18·75 (LMC) and 19·2 (SMC). The colours of SMC cepheids are 0.m1 bluer than those in the Galaxy and they may be somewhat underluminous for their periods.

Further Observations of Magellanic Cloud Cepheids

Two-colour light-curves have been obtained, mostly by photoelectric photometry, for 13 SMC and 7 LMC cepheids, with periods in the range 1.24 to 6.69 days. The following P–L and P–C relations were found: |$LMC: \langle V \rangle = 17.58 - 3.072 \,\text{log} P$| |$\langle B \rangle -\langle V \rangle = 0.49 + 0.191 \,\text{log} \,P$| |$\text{SMC:} \langle V \rangle = 17.73 - 2.879 \,\text{log} \,P$| |$\langle B \rangle - \langle V \rangle = 0.26 + 0.306 \,\text{log} \,P$| The 25 SMC, 18 LMC and 13 galactic cepheids for which the appropriate data are available also obey, to within observational error, the Sandage relation |$\langle V \rangle = a-3.609 \,\text{log} P + 2.52 (\langle B \rangle - \langle V \rangle)$| where a = – 2.33 for the galactic cepheids, 17.03 for the SMC, and 16.40 for the LMC. This implies moduli for 18.73 for the LMC and 19.36 for the S.M. C. Reddening has been estimated from the colours of field B-stars, mostly faint. We found 0.02 for the SMC and 0.05 for the LMC. With this reddening the SMC cepheids are in the mean about 0.1 mag bluer than those in the Galaxy, as opposed to the 0.2 found previously. Some implications of the above results are briefly discussed.