Cepheid Mass Research Articles

The effective temperatures, radii and masses of Dwarf Cepheids

Using the flux values determined with the infrared flux method (IRFM) developed by Blackwell and Lynas-Gray (1993), we derived the empirical relationship between flux (F v ) and (V — K) colour appropriate to Dwarf Cepheids. For three Dwarf Cepheids CY Aqr, YZ Boo and SZ Lyn where both VK photometry and radial velocities were available from the literature, effective temperatures were determined using the intrinsic Stromgren indices, model atmosphere grids for (V — K) and the relation between temperature and (V — K) colour. Then, by applying the infrared surface brightness method, radii and distances and hence masses and absolute magnitudes were estimated with effective temperatures determined by three different methods. It was found that the average mass of these variables is about 0.5 solar mass and this result supports the hypothesis that Dwarf Cepheids are pre-white dwarf objects. It was also confirmed that the temperatures determined with the IRFM are most successful in the application of the surface brightness method to the radius estimation of Dwarf Cepheids.

The mass ratios of Cepheid binaries

The distribution of mass ratios in binary systems is important for comparison with star formation calculations but has been difficult to obtain observationally. This study uses IUE spectra of the hot companions of classical Cepheids with observed orbital motion to determine the companion types and hence their masses. Combining these with Cepheid masses inferred from an appropriate mass-luminosity relation produces a distribution of mass ratios q = M<SUB>2</SUB>/M<SUB>1</SUB> (where M<SUB>1</SUB> is the mass of the Cepheid). This is a distribution of spectroscopic (as opposed to dynamic) mass ratios for intermediate-mass stars with orbital periods longer than a year. The distribution is strongly peaked to low-mass companions. The IUE spectra can detect companions in systems with mass ratios as small as 0.26. Incompleteness in detecting low-amplitude orbital motion means the concentration to low masses is even larger than that in the observed distribution. The fact that the orbital periods are longer than one year, and only one eccentricity is zero, implies that it is unlikely that there has been mass transfer between the components in the systems, except possibly in one case.

Independent distance determinations to Milky Way Cepheids in open clusters and associations. 1: The binary Cepheid DL CAS in NGC 129

view Abstract Citations (11) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Independent Distance Determinations to Milky Way Cepheids in Open Clusters and Associations. I. The Binary Cepheid DL CAS in NGC 129 Gieren, Wolfgang P. ; Welch, Douglas L. ; Mermilliod, Jean-Claude ; Matthews, Jaymie M. ; Hertling, Gisela Abstract As an eight-day Cepheid which is both a component of a spectroscopic binary and a member of the open cluster NGC 129, DL Cas is potentially a very accurate calibrator of the period-luminosity (PL) relation and Cepheid mass. From 160 high-precision (sigma less than 1.5 km/s) radial velocity observations made with the CORAVEL and DAO spectrometers -- including 67 new unpublished data -- we have obtained both the orbital and pulsational velocity curves of this binary Cepheid. This body of RV data makes DL Cas one of the best observed Cepheids in our galaxy. Our analysis yields an orbital period of 684.4 +/- 0.4 days which confirms DL Cas as one of the shortest-period binaries containing a Cepheid. We derive new precise orbital elements which replace earlier preliminary values found by Harris et al. Isochrone fitting to the V, B - V data points of Turner et al. yields an age of NGC 129 of (7.6 +/- 0.4) x 107 yr and a Cepheid mass of 5.6 solar mass. Evidence from age, a possible period change, and strip crossing times suggest that DL Cas is a solar-abundance star making its third (redward) crossing through the Cepheid instability strip. Existing observational constraints from our mass function of the DL Cas system and an International Ultraviolet Explorer (IUE) spectrum suggest that the companion is a main sequence star in the mass range from 2.6 to 5.6 solar mass. We use the pulsational velocity curve and published photometry to derive the distance and mean radius of DL Cas with the surface brightness method, finding values of 2034 +/- 110 pc and 66.0 +/- 3.5 solar radius, respectively. The radius we derive indicates that DL Cas is a fundamental-mode pulsator, removing any possible ambiguity in mode identification. The distance corresponds to a mean absolute visual magnitude of (MV) = -4.2 +/- 0.3 mag whose error is dominated by the uncertainty of the absorption correction. Since our very precise distance contributes only 0.12 mag to the error in (MV), improved reddening studies of NGC 129 would make DL Cas a very tight calibrator of the PL relation. Our value of the gamma velocity of the DL Cas system is identical to the mean radial velocity of the stars in NGC 129, strengthening the case for cluster membership. However, our distance for DL Cas, and thus for NGC 129, is significantly larger than the 1670 +/- 13 pc obtained by Turner et al. from Zero Age Main Sequence (ZAMS) fitting of the cluster. Possible causes for this discrepancy, and their implications for Cepheid distance scale calibrations, are discussed. Publication: The Astronomical Journal Pub Date: June 1994 DOI: 10.1086/117019 Bibcode: 1994AJ....107.2093G Keywords: Cepheid Variables; Distance; Milky Way Galaxy; Open Clusters; Star Clusters; Brightness Distribution; Stellar Spectrophotometry; Astronomy; OPEN CLUSTERS AND ASSOCIATIONS: INDIVIDUAL: NGC 129; CEPHEIDS full text sources ADS | data products SIMBAD (2) CDS (1) Related Materials (2) Part 2: 1995AJ....110.2280M Part 3: 1996AJ....111.2059G

The distance to the Large Magellanic Cloud - Constraints from Cepheids in Large Magellanic Cloud star clusters

We have used recent observational data for the Cepheids in the rich, young Large Magellanic Cloud clusters NGC 1866 and NGC 2031 to constrain the cluster distances with the mass-equivalency (ME) method. The basis of this approach is to fix the cluster distances by requiring the Cepheid evolutionary and pulsational masses to be equal. Using evolutionary models incorporating a mild amount of core and envelope over-shooting along with recent pulsational models, we derive distance moduli of 18.51 +/- 0.21 and 18.32 +/- 0.20 for NGC 1866 and NGC 2031, respectively. The quoted errors are dominated by the uncertainties in the heavy element abundances of the clusters (assumed to be 0.3 dex for both clusters), with a smaller contribution due to the apparently intrinsic spread in the masses of the Cepheids in each cluster. For the ME method, we find that {DELTA}(m - M)-0_/δZ_1_ = 0.69, where Z_1_ = log (Z/0.016). This result implies that the cluster distances can be determined to better than +/- 5% if the cluster abundances can be measured to better than about +/- 0.15 dex. The distance moduli we derive for NGC 1866 and NGC 2031 are consistent with other recent values derived for the LMC, meaning that the models used in this analysis avoid the classical evolutionary/pulsational Cepheid mass discrepancy. The results of our analysis are based on models using the Los Alamos opacities; had we used models incorporating the new Livermore opacities instead, we estimate that the cluster distance moduli would be larger by at most 0.1 mag.

Comparative Pulsation Calculations with OP and OPAL Opacities

The OPAL opacities (Iglesias and Rogers 1991; Iglesias, Rogers and Wilson 1992) are recent revisions to the traditional Los Alamos (LA) opacities and have proven very successful in resolving the Cepheid beat mass, and to a lesser extent, the Cepheid bump mass discrepancies (Moskalik, Buchler and Marom 1991, hereafter MBM). MBM showed that for the beat Cepheids the P1/P0 period ratios, calculated with OPAL, yielded solar masses between 4 and 7, in agreement with other mass determinations. MBM also found that the P2/P0 period ratios were reduced, implying higher bump Cepheid masses, though the conflict with standard evolutionary masses was not completely eliminated. We have made linear nonadiabatic pulsation calculations with another set of recently computed opacities, namely those of the Opacity Project (Seaton 1987, 1992, hereafter OP). Since the two teams have employed different techniques in their calculations, it is of interest to compare pulsation results using the two sets of opacities.

Absorption-line profiles in a companion spectrum of a mass-losing cool supergiant

Cool star winds can best be observed in resonance absorption lines seen in the spectrum of a hot companion, due to the wind passing in front of the blue star. We calculated absorption line profiles that would be seen in the ultraviolet part of the blue companion spectrum. Line profiles are derived for different radial dependences of the cool star wind and for different orbital phases of the binary. Bowen and Wilson find theoretically that stellar pulsations drive mass loss. We therefore apply our calculations to the Cepheid binary S Muscae which has a B5V companion. We find an upper limit for the Cepheid mass loss of M less than or equal to 7 x 10 (exp -10) solar mass per year provided that the stellar wind of the companion does not influence the Cepheid wind at large distances.

Toward a resolution of the bump and beat Cepheid mass discrepancies

The extant beat and bump Cepheid mass discrepancy problems are reexamined with the new opacities of Iglesias and Rogers. Compared to calculations with the Los Alamos opacities, the period ratios P 1 /P 0 and P 2 /P 0 (1) are strongly reduced for any fixed stellar parameters (L, M, T eff , X, Z) and (2) exhibit a novel, large sensitivity to luminosity and to metallicity. For the beat Cepheids the P 1 /P 0 period ratios now yield masses between 4 and 7 M ⊙ , in agreement with the other mass determinations

The mass of the classical Cepheid SU Cygni

Radial velocity differences between the classical Cepheid SU Cyg and a hot companion have been measured from IUE high dispersion spectra. The blue star is itself a member of a close binary system. The triple system solution provides the ratio of the Cepheid mass to the sum of the masses of the companions. IUE low dispersion spectra are used to infer the masses of the companions. A mass of 6.3 M⊙ is derived for the Cepheid, with a range from 7.0 M⊙ to 5.9 M⊙, which is in agreement with the evolutionary mass.

The dynamical mass of S MUSCAE

The amplitudes and phase relations of pulsational velocities of the Cepheid S Muscae, measured for lines originating at different atmospheric depths, are investigated. A mass M(A) = 4.4 + or - 0.5 solar masses is found for the Cepheid; however, the Cepheid is the evolved star and should have a mass larger than that of its companion. If the measured velocity differences are too low by 2.5 km/s on the average, then the mass ratio M(B)/M(A) may be decreased to 0.94, giving an estimated upper limit to the Cepheid mass of 6.1 solar masses, consistent with the Cepheid being the more evolved star. Considering all the uncertainties, it is concluded that the mass of the Cepheid is between 4.6 and 6.1 solar masses.

Pulsations of Eötvös Spheres

AbstractA derivation of Eötvös spheres and their pulsations is presented. These spheres incorporate a short range force in their gravitational potential. We used a Yukawa formulation to agree with other workers in this field, although a slightly different form would guarantee a gravitational force that is always attractive. Various relationships are obeyed by these obejcts, much like the polytropes to which they are similar. An attempt is made to test whether a short range force can resolve two outstanding problems in astrophysics. These are the Cepheid mass discrepancy and the frequencies of high-order solar p-modes. The disagreement in predicted and observed Cepheid masses cannot be explained by a repulsive force, but the solar p-modes have their asympotoic frequency decreased. Linear fits to sequences of models are presented for the radial eigenfrequencies and asymptotic frequencies for nonradial pulsations.

Classical bump Cepheids - Reconciliation of theory with observations

view Abstract Citations (28) References (145) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Classical Bump Cepheids: Reconcilliation of Theory with Observations Carson, T. Richard ; Stothers, Richard B. Abstract New models of classical bump Cepheids lying along the Cepheid ridge line in the H-R diagram are computed to obtain a more accurate set of predicted surface velocity curves. Acceptable Cepheid models are found to be 0.5 mag brighter at a fixed stellar mass than standard evolutionary models. All the previously obtained manifestations of the Cepheid mass discrepancy, except for the anomalous double-mode Cepheid masses, are resolved, at least in a statistical sense, by accepting the implied luminosity increase. The need for the luminosity increase is independently inferred from standard evolutionary models of intermediate-mass and high-mass giant and supergiant stars from their location in the observational H-R diagram. Publication: The Astrophysical Journal Pub Date: May 1988 DOI: 10.1086/166281 Bibcode: 1988ApJ...328..196C Keywords: Cepheid Variables; Hertzsprung-Russell Diagram; Stellar Interiors; Stellar Luminosity; Stellar Oscillations; Binary Stars; Statistical Analysis; Stellar Evolution; Stellar Mass; Supergiant Stars; Astrophysics; OPACITIES; STARS: CEPHEIDS; STARS: INTERIORS; STARS: LUMINOSITIES; STARS: PULSATION full text sources ADS | data products SIMBAD (44)

Observational evidence for mass loss from classical Cepheids

This paper examines the evidence for mass loss from classical Cepheid variables in the light of recent observational studies of infrared and ultraviolet emission from these objects. Mass-loss rates derived for several stars range between |$10^{-10}M_\odot \text{yr}^{-1}$| and |$10^{-10}M_\odot \text{yr}^{-1}$|⁠. The lower end of this range probably corresponds to the majority of classical Cepheids. Non-variable supergiants show, on average, a somewhat lower rate of infrared excess, but have mass-loss rates of the same order of magnitude as the Cepheids. On the basis of the observations to date, mass loss alone is insufficient in explaining the Cepheid mass discrepancy, indicating that adjustments to the evolutionary or pulsation models present a better prospect of resolving this discrepancy.

Are most short-period Cepheids overtone pulsators?

Data given and analyzed recently by Coulson et al. (1986) and Gieren (1982) provide a consistent set of Wesselink radii and Wesselink masses, for which the internal error bars appear to be small enough that a quantitative discussion appears to be warranted. When it is assumed that all Cepheids pulsate in the fundamental mode, a steep discontinuity in mass is found for periods around 6.5 days. When short-period Cepheids are interpreted as first-overtone pulsators as required theoretically (Christy, 1966; Stobie, 1969), the discontinuity disappears and the mass-period relation passes through the bump and beat masses for Cepheids.

Cepheid radii and masses from the surface-brightness method

Simultaneous BVRI photometric and radial-velocity observations of some 30 galactic Cepheids are used to derive their radii using the surface-brightness method of Barnes & Evans. A period–radius relationship is obtained from these data which is compared to those radii obtained from other methods. Pulsation masses based on the new radii are calculated and compared to the theoretical masses of the stars. It is found that the period–radius relationship obtained from surface-brightness radii agrees essentially with the one derived from the cluster Cepheids if the fainter Cepheid luminosities advocated by Schmidt, Bohm-Vitense, and Gieren are used. Wesselink radius determinations using the (B−V) colour index which do not correct for colour–colour loops appear to seriously underestimate the true Cepheid radii for long-period stars. Pulsation masses calculated from the surface-brightness radii show bad agreement with theoretical masses for short-period Cepheids, but increasingly better agreement for long-period stars. This is contrary to earlier findings. The present results indicate that most long-period Cepheids are high-mass stars, contrary to a recent suggestion of Böhm-Vitense that a large portion of long-period Cepheids are actually low-mass stars on high-luminosity crossings through the instability strip.

Evidence for mass loss from IRAS observations of classical Cepheids

Mass loss from classical Cepheid variables is suspected on two grounds. First, it may provide an explanation of the persistent discrepancy between estimates of Cepheid masses based on the theories of stellar pulsation and of stellar evolution1. Second, theoretical models of pulsating atmospheres2 suggest that a pulsation mechanism may be responsible for causing, or enhancing, mass loss from Cepheids. In order to test these hypotheses, evidence of anomalous mass loss was sought by making a comparison between the infrared emission of Cepheids and that of nonvariable supergiants in the same luminosity and effective temperature range. A search of the IRAS (Infrared Astronomy Satellite) catalogue3 found a number of Cepheids and stable supergiants which showed emission in at least one of the IRAS wavelength bands. Some long-period Cepheids showed infrared excesses with respect to their non-pulsating counterparts, while emission from Cepheids with periods of less than 10 days was comparable to the levels seen in the stable supergiants. Mass loss rates of up to 7 × 10−7 M⊙ yr−1 were derived from the infrared excesses, which is sufficiently high to have a major effect on the evolution of these stars.

A photometric and radial velocity study of six southern Cepheids. II - Binarity, radii, luminosities, and masses

view Abstract Citations (29) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Photometric and Radial Velocity Study of Six Southern Cepheids. II. Binarity, Radii, Luminosities, and Masses Coulson, I. M. ; Caldwell, J. A. R. ; Gieren, W. P. Abstract The data now available for the Galactic Cepheids AQ Car (period = 9.77 days), XX Cen (10.95 days), XY Car (12.44 days), TT Aql (13.75 days), XX Car (15.71 days), and XZ Car (16.65 days) are analyzed for binarity, radius, luminosity, and mass. There is weak evidence only for binarity of XX Cen, XX Car, and XZ Car, and it is concluded that all six Cepheids may be considered to be single. The new velocity data for XX Cen suggest that it may belong to a binary system with an orbital period of 800 d. The radii are derived by an improved version of the Baade-Wesselink technique and are found to depend upon the color index used to define the surface brightness. The V - I radii, for instance, are 20-25 percent larger than the B - V radii, and it is suggested that the Cepheid mass discrepancy problem may be alleviated by use of appropriate colors in the B - W radius solutions. Publication: The Astrophysical Journal Pub Date: April 1986 DOI: 10.1086/164072 Bibcode: 1986ApJ...303..273C Keywords: Binary Stars; Cepheid Variables; Radial Velocity; Stellar Luminosity; Stellar Mass; Stellar Spectrophotometry; Astrometry; Mass To Light Ratios; Milky Way Galaxy; Orbital Elements; Radii; Southern Sky; Stellar Color; Astrophysics; STARS: BINARIES; STARS: CEPHEIDS; STARS: PULSATION full text sources ADS | data products SIMBAD (6) Related Materials (1) Part 1: 1985ApJS...57..595C

The Cepheid mass problem and Cepheid binaries

Existing mass determinations for Cepheids with different periods are examined. Wesselink masses are independent of the adopted distance scale. For short periods (less than 6 days) they follow the sequence of evolutionary masses. For periods longer than 10 days they are lower by up to a factor of 2. The lower mass branch joins up with the bump masses. The new pulsational masses agree with the Wesselink masses for periods longer than 6 days. Cepheid masses determined by means of their giant companions also agree with the Wesselink masses and the new pulsational masses. While the error bars are large, the derived dynamical masses determined for S Mus and V636 Sco also agree with the low Wesselink and giant companion masses.

Some Masses For Population I and II Cepheids

The masses of Cepheids can be obtained in several ways. If a Cepheid luminosity is known from membership in a galactic cluster, the mass-luminosity relation obtained from stellar evolution theory gives its mass. This evolution mass depends slightly on the composition, that is, the mass fraction of helium, Y, and on the the mass fraction of all the heavier elements, Z, but as we shall see later, the composition dependence is small.

Duplicity, Mass Loss and the Cepheid Mass Anomaly

The rate of binaries among cepheid stars is 25 - 35% (Burki, 1984a), a value which is in agreement with the rate among F-M supergiants (31-38%) obtained by Burki and Mayor (1983) from a radial velocity survey.For binary cepheids, the Wesselink radius RW is affected by the light of the companion. Balona (1977) found that RW is too small if the companion is a blue main sequence star and too large if it is a red giant star. This effect has been quantitatively examined by Burki (1984a). For example, it was found that, in the case of a cepheid of period P = 32d with a companion fainter by 2 mag., RW is 70% of its correct value if we are dealing with a main sequence companion and 130% in the case of a companion redder by 0.6 in B-V. The bias on RW becomes negligible when the companion is fainter than the cepheid by more than 4 mag.

The luminosity scale of Cepheid variable stars - A revison

The period-luminosity color (PLC) relation for classical Cepheids is discussed in terms of a recent redetermination of the distance moduli of open clusters with Cepheid members. The distance moduli of eight clusters with well-established Cepheid members were determined from Stromgren four-color and H-beta photometry of the B stars. Possible sources of systematic errors in these distance moduli are discussed. Zero points are derived from these data for the PLC relation on the UBV system and the period-luminosity relations for near-infrared magnitudes. The present relations yield absolute magnitudes which are fainter by 0.4-0.6 mag than those now commonly used. These lower luminosities cause the pulsational masses of the Cepheids to be less than the evolutionary masses by up to a factor of 2.5 but bring them into good agreement with the masses of beat and bump Cepheids.