Nancy Evans

S Mus if the Cepheid with the hottest known companion. As a benefit, the large ultraviolet flux made it the only Cepheid companion for which the velocity amplitude could be measured with the echelle mode of the HST GHRS. Unfortunately, the high temperature is difficult to constrain at wavelengths longer than 1200 Å because of the degeneracy between temperature and

S Mus if the Cepheid with the hottest known companion. As a benefit, the large ultraviolet flux made it the only Cepheid companion for which the velocity amplitude could be measured with the echelle mode of the HST GHRS. Unfortunately, the high temperature is difficult to constrain at wavelengths longer than 1200 Å because of the degeneracy between temperature and

S Mus if the Cepheid with the hottest known companion. As a benefit, the large ultraviolet flux made it the only Cepheid companion for which the velocity amplitude could be measured with the echelle mode of the HST GHRS. Unfortunately, the high temperature is difficult to constrain at wavelengths longer than 1200 Å because of the degeneracy between temperature and

Polaris is the luminous component of a multiple system with at least 3 members. A marginal ROSAT HRI source has been found close to a fourth possible component. A 10 ksec Chandra ACIS exposure will establish whether this star produces X-rays, and hence is young and probably a companion of Polaris. Would this companion (5000 AU from Polaris) have been retained if the system were ejected from a cluster? Or is there a cluster of low mass stars still around Polaris? Finally, the ACIS low resolution spectrum of Polaris itself will determine whether X-rays are produced by the supergiant (comparatively soft) or a main sequence companion (much harder). A second observation (Delta Cephei) will tell us whether the amplitude of pulsation affects magnetic phenomena.

The Cepheid-period luminosity relation is a primary distance indicator in extragalactic studies. It is an important tool in studies of young stars, star formation, and abundances in nearby galaxies, as well as a test of models of stellar evolution and pulsation. This proposal introduces binary Cepheids as the first new class of Cepheid luminosity calibrators since cluster Cepheids. IUE LWP and SWP spectra can be used to derive all four parameters needed to obtain an absolute magnitude for a Cepheid from the absolute magnitude of the blue companion: the magnitude difference between the two stars, the temperature of the companion, the luminosity of the companion, and the reddening of the system. As described below, IUE spectra are the only way to derive a magnitude difference and the temperature of the companion. In addition, the investigation of the reddening by studying the spectrum of the companion in the 2200 A region provides a new check of the Cepheid reddening scale. Previous IUE studies have obtained spectra of 18 Cepheid/companion pairs. However, no previous study has derived the magnitude differences between the stars, and thus made possible the use of binary Cepheids as luminosity calibrators.

Polaris has a spectroscopic orbit determined from an extensive series of observations as well as a more uncertain astrometric orbit. The determination of its mass and evolutionary state is of considerable interest because it is a low-amplitude classical Cepheid with unusual period and amplitude variations. In this study, IUE spectra are investigated to search for light from the companion. The spectra of Polaris from 1600 A to 3200 A are a good match for nonvariable supergiants of similar spectral type. The lack of any excess flux at the shortest wavelengths implies that a main-sequence companion must be later than A8 V. Although this is the most likely companion, the ultraviolet observations cannot rule out a white dwarf 15,000 K or cooler. Both these companions are consistent with either an evolutionary mass or a smaller pulsation mass for the Cepheid.

We report on the analysis of an archival observation of part of the {\alpha} Persei cluster obtained with XMM-Newton. We detected 102 X-ray sources in the band 0.3-8.0 keV, of which 39 of them are associated with the cluster as evidenced by appropriate magnitudes and colors from 2MASS photometry. We extend the X-ray Luminosity Distribution (XLD) for M dwarfs, to add to the XLD found for hotter dwarfs from spatially extensive surveys of the whole cluster by ROSAT. Some of the hotter stars are identified as a background, possible slightly older group of stars at a distance of approximately 500 pc.

ABSTRACT We have observed the double cluster h and chi Per with the ROSAT PSPC for 11 ksec. Emission is concentrated toward the two cluster centers, however the resolution at the distance of the clusters (2.4 kpc) is too poor to say whether the emission is diffuse or from a population of unresolved faint sources. 30 sources were found (at the 2.5 sigma level), with an X-ray luminosity of log L = 31.5 ergs sec(-1) or greater. These sources occur in the cluster nuclei, between the clusters and in the halo around the cluster pair. Individual optical sources cannot be identified, but because of the lack of correlation between the X-ray sources and B stars, we conclude that the X-rays are produced by late spectral type pre-main sequence stars. The X-ray sources are brighter than all but the brightest sources in the younger Orion Nebula cluster. These h and chi sources may represent the peak X-ray flux prior to the main sequence when stars have spun up more than the Orion Nobula stars but have still not fully contracted to the main sequence.

Binary/multiple status can affect stars at all stages of their lifetimes: evolution onto the main sequence, properties on the main sequence, and subsequent evolution. 5 Msolar stars have provided a wealth of information about the binary properties fairly massive stars. The combination of cool evolved primaries and hot secondaries in Cepheids (geriatric B stars) have yielded detailed information about the distribution of mass ratios. and have also provided a surprisingly high fraction of triple systems. Ground-based radial velocity orbits combined with satellite data from Hubble, FUSE, IUE, and Chandra are needed to provide full information about the systems, including the masses. As a recent example, X-ray observations can identify low mass companions which are young enough to be physical companions. Typically binary status and properties (separation, eccentricity, mass ratio) determine whether any stage of evolution takes an exotic form.

The Stellar Imager mission concept is a space-based UV/Optical interferometer designed to resolve surface magnetic activity and subsurface structure and flows of a population of Sun-like stars, in order to accelerate the development and validation of a predictive dynamo model for the Sun and enable accurate long-term forecasting of solar/stellar magnetic activity.

Absolute magnitudes for binary classical Cepheids were derived by ratioing IUE low dispersion spectra in regions where the blue companion dominates with spectra of main sequence spectral type standards. The IUE spectra are also used to determine the magnitude difference between the Cepheid and the blue companion. Absolute magnitudes determined for SU Cyg and W Sgr agree with the absolute magnitudes of Sandage and Tammann and Caldwell within the + or - 0m2 estimated uncertainty, but not with the fainter absolute magnitudes of Schmidt. The absolute magnitude of SU Cas is in better agreement with the PLC relations if it is pulsating in the first overtone mode.

The low-resolution X-ray spectra around η Car covering Trumpler 16 and part of Trumpler 14 have been extracted from a Chandra CCD ACIS image. Various analysis techniques have been applied to the spectra based on their count rates. The spectra with the greatest number of counts (HD 93162 = WR 25, HD 93129 AB, and HD 93250) have been fitted with a wind model, which uses several components with different temperatures and depths in the wind. Weaker spectra have been fitted with Raymond-Smith models. The weakest spectra are simply intercompared with strong spectra. In general, fits produce reasonable parameters based on knowledge of the extinction from optical studies and on the range of temperatures for high- and low-mass stars. Direct comparisons of spectra confirm the consistency of the fitting results and also hardness ratios for cases of unusually large extinction in the clusters. The spectra of the low-mass stars are harder than the more massive stars. Stars in the sequence evolving from the main sequence (HD 93250) through the system containing the O supergiant (HD 93129 AB) and then through the Wolf-Rayet stage (HD 93162), presumably ending in the extreme example of η Car, share the property of being unusually luminous and hard in X-rays. For these X-ray-luminous stars, their high mass and evolutionary status (from the very last stages of the main sequence and beyond) is the common feature. Their binary status is mixed, and their magnetic status is still uncertain. Based on observations made with the Chandra X-Ray Observatory.

We have obtained medium-resolution spectra (lambda/Deltalambda ~ 20,000) of the hot binary companion to the classical Cepheid U Aql with the Goddard High Resolution Spectrograph on the Hubble Space Telescope (HST). These have been used to determine the orbital velocity amplitude. Combining this with the orbital velocity amplitude of the Cepheid from the ground-based orbit and the mass of the companion inferred from its spectral type, we measure a mass of the Cepheid of 5.1 +/- 0.7 M&sun;. We discuss the full sample of Cepheids for which we have determined masses with HST (S Mus, V350 Sgr, Y Car, and U Aql) and also SU Cyg (mass from IUE). The HST masses are in agreement with the luminosities predicted by recent evolutionary tracks with moderate overshoot. This comparison, however, may be altered by reassessment of Cepheid distances based on Hipparcos parallaxes. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NASA-26555.

The region around the $\eta$ Car nebula has three OB associations, which contain a Wolf-Rayet star and several massive O3 stars. An early Chandra ACIS-I image was centered on $\eta$ Car and includes Trumpler 16 and part of Trumpler 14. The Chandra image confirms the well-known result that O and very early B stars are X-ray sources with L$_X$ $\simeq$ 10$^{-7} \times$ L$_{bol}$ over an X-ray luminosity range of about 100. Two new anomalously strong X-ray sources have been found among the hot star population, Tr 16-244, a heavily-reddened O3 I star, and Tr 16-22, a heavily-reddened O8.5 V star. Two stars have an unusually large L$_X$/L$_{bol}$: HD 93162, a Wolf-Rayet star (and possible binary), and Tr 16-22, a possible colliding wind binary In addition, a population of sources associated with cool stars is detected. In the color-magnitude diagram, these X-ray sources sit above the sequence of field stars in the Carina arm. The OB stars are on average more X-ray luminous than the cool star X-ray sources. X-ray sources among A stars have similar X-ray luminosities to cooler stars, and may be due to cooler companions. Upper limits are presented for B stars which are not detected in X-rays. These upper limits are also the upper limits for any cool companions which the hot stars may have. Hardness ratios are presented for the most luminous sources in bands 0.5 to 0.9 keV, 0.9 to 1.5 keV, and 1.5 to 2.04 kev. The available information on the binary nature of the hot stars is discussed, but binarity does not correlate with X-ray strength in a simple way.

Polaris has presented us with the rare phenomenon of a Cepheid with a pulsation amplitude that has decreased over the last 50 yr. In this study we have used this property to see whether the amplitude decrease during the last 15 yr has had any effect on upper atmosphere heating. We obtained IUE high and low-resolution spectra but found no change in either the Mg II chromospheric emission or the flux at 1800 A between 1978 and 1993 when the pulsation amplitude dropped by 50% (from 2.8 to 1.6 km/s). The energy distribution from 1700 A through V, Be, R(KC), and I(KC) is like that of a nonvariable supergiant of the same color rather than a full amplitude Cepheid in that it has more flux at 1800 A than the full amplitude Cepheid delta Cap. Polaris also has a rapidly changing period (3.2 s/yr), in common with other overtone pulsators. We argue that this is a natural consequence of the different envelope locations that dominate pulsation growth rates in fundamental and overtone pulsation. In fundamental mode pulsators, the deeper envelope is more important in determining growth rates than for overtone pulsators. For fundamental mode pulsators, evolutionary changes in the radius produce approximately linear changes in period. In overtone pulsators, pulsation reacts to small evolutionary changes in a more unstable way because the modes are more sensitive to high envelope features such as opacity bumps, and the growth rates for the many closely spaced overtone modes change easily. Finally, the upper limit to the X-ray flux from an Einstein observation implies that the companion in the astrometric orbit is earlier than FAA V. The combination of upper and lower limits on the companion from IUE and Einstein respectively catch the companion mass between 1.7 and 1.4 solar mass. The X-ray limit is consistent with the more distant companion alpha UMi B being a physical companion in a hierarchal triple system. However the X-ray limits require that the even more distant companions alpha UMi C and D are too old to be physically associated with Polaris.

The determination of accurate masses for Cepheid variable stars is required for quantitative understanding of these primary distance indicators, and also the related questions of the accuracy of evolutionary calculations and the role played by massive stars in galactic evolution. The system ADS 14859 = HR 8157 = V1334 Cyg provides a unique opportunity to determine a Cepheid mass because it has a visual binary orbit. The system consists of a wide pair {AB} discovered by Hough {1887}, and a newly discovered close system {Aa, b} which consists of the Cepheid {Aa} and a yet uncharacterized companion {Ab}. No mass information will be available, however, without the proposed HST FGS and STIS observations, particularly of the Ab star which cannot be observed from the ground. From the STIS observations we will determine the temperature and infer the mass of Ab. Combining this mass with the sum of all three masses of the system derived from the visual orbit and the mass of B from IUE observations provides the mass of the Cepheid {Aa}. In addition, the FGS observations {POS mode} of the Aa, b system can provide its inclination, and hence the sum of the two masses of that system, and ultimately the Cepheid mass. Furthermore, the short period system {Aa, b} should be resolvable with the improved FGS in TRANS mode. Thus, the combination of these observations will provide determinations of the Cepheid mass from both the close and wide orbits.

Deriving the distribution of binary parameters for a particular class of stars over the full range of orbital separations usually requires the combination of results from many different observing techniques (radial velocities, interferometry, astrometry, photometry, direct imaging), each with selection biases. However, Cepheids---cool, evolved stars of $\sim$$5\, M_\odot$---are a special case because ultraviolet spectra will immediately reveal any companion star hotter than early type A, {\it regardless of the orbital separation}. We have used {\it International Ultraviolet Explorer} (\IUE) UV spectra of a complete sample of all 76 Cepheids brighter than V=8 to create a list of {\it all 18} Cepheids with companions more massive than $2.0\, M_\odot$. Orbital periods of many of these binaries are available from radial-velocity studies, or can be estimated for longer-period systems from detected velocity variability. In an imaging survey with the {\it Hubble Space Telescope} Wide Field Camera 3, we resolved three of the companions (those of $\eta$ Aql, S Nor, and V659 Cen), allowing us to make estimates of the periods out to the long-period end of the distribution. Combining these separations with orbital data in the literature, we derive an unbiased distribution of binary separations, orbital periods, and mass ratios. The distribution of orbital periods shows that the $5\, M_\odot$ binaries have systematically shorter periods than do $1\, M_\odot$ stars. Our data also suggest that the distribution of mass ratios depends both on binary separation and system multiplicity. The distribution of mass ratios as a function of orbital separation, however, does not depend on whether a system is a binary or a triple.

File ob78_2.dat contains 64 X-ray spectral parameters used for the 78 O- and early-B stars with determined spectral types and more than 50 net counts in the Chandra Carina Complex Project (Townsley+, 2011ApJS..194....1G). Lbol values are from Povich et al. (2011, Cat. J/ApJS/194/6). Spectral types from Gagne et al. (2001, Cat. J/ApJS/194/5). See also Broos et al, (2001, Cat. J/ApJS/194/2) (8 data files).

Observations obtained at the Dominion Astrophysical Observatory are used to derive a spectroscopic orbit for AW Per. Orbital elements calculated include a period of 13,100 + or - 1000 days and a mass function for the orbits of 1.17 + or - 0.30 solar masses. The present orbit is shown to be consistent with the phase residuals in the O-C diagram found by Evans (1983) and Szabados (1980).

We report analysis of Chandra observations of h Persei, part of the famous Double Cluster h and chi Persei. At 13-14 Myr-old,h Persei probes ages during which terrestrial planets are potentially in the final stages of formation and when nebular gas has recently dissipated, leaving newly-formed gas giants unshielded from high energy X-ray photons. We find a large number of Chandra-detected sources have optical/IR counterparts whose positions on V/V-I color-magnitude diagrams are consistent with cluster membership. At least 3 of these sources have weak warm dust emission indicative of terrestrial planet formation. We have detected sources down to log Lx = 30.0 ergs/s but presumably this is the bright edge of a much larger X-ray population. We discuss h Persei in the context of other Chandra-observed clusters and briefly discuss the effect that X-rays play in driving grain chemical reactions and oblating planetary atmospheres. Funding for this work was provided by Chandra grant 16617421 and Chandra X-ray Center NASA Contract NAS8-39073.

γ Cas is the prototypical classical B0.5e star and is now known to be the primary in a wide binary system. It has long been famous for its unique hard X-ray characteristics, among which are variations that correlate with changes in a number of optical light and UV line and continuum properties. These peculiarities have led to a picture in which processes on or near the Be star produce the observed X-ray emission. In this paper we report on a 53 ks Chandra High Energy Transmission Grating Spectrometer observation of this target. An inspection of our spectrum shows that it is quite atypical for a massive star. The emission lines appear weak because of a strong short-wavelength continuum that arises from a hot plasma with kT=11-12 keV. The spectrum exhibits many lines, the strongest of which are Lyα features of H-like species from Fe through the even-Z intermediate elements (S, Si, Mg, and Ne), down to O and N. Line ratios of the ``rif triplet'' for a variety of He-like ions and of Fe XVII are consistent with the dominance of collisional atomic processes. However, the presence of Fe and Si fluorescence K features indicates that photoionization also occurs in nearby cold gas. The line profiles indicate a mean velocity at rest with an rms line broadening of 500 km s-1 and little or no asymmetry. An empirical global-fitting analysis of the line and continuum spectrum suggests that there are actually three or four plasma emission components. The first is the dominant hot (12 keV) component, of which some fraction (10%-30%) is heavily absorbed, while the remainder is affected by a much lower column density of only 3×1021 cm-2. The hot component has a Fe abundance of only 0.22+/-0.05 solar. The other two or three major emission components are ``warm'' and are responsible for most other emission lines. These components are dominated by plasma having temperatures near 0.1, 0.4, and 3 keV. Altogether, the warm components have an emission measure of about 14% of the hot component, a low column density, and a more nearly solar composition. The 100 eV component is consistent with X-ray temperatures associated with a wind in a typical early B star. Nonetheless, its emission measure is a few times higher than would be expected from this explanation. The strength of the fluorescence features and the dual-column absorption model for the hot plasma component suggest the presence near the hot sites of a cold gas structure with a column density of ~1023 cm-2. Because this is also the value determined by Millar and Marlborough for the vertical column of the Be disk of γ Cas, these attributes suggest that the X-ray-emitting sources could be close to the disk and hence to the Be star. Finally, we discuss the probably related issues of the origin of the warm emission components, as well as the puzzling deficient Fe abundance in the hot component. It is possible that the latter anomaly is related to the FIP (abundance fractionation) effect found in certain coronal structures on the Sun and RS CVn stars. This would be yet another indication that the X-rays are produced in the immediate vicinity of the Be star.

We have observed the small-amplitude Cepheid V1334 Cyg A (pulsation period 3.3 days) for nearly 30 years. From these radial velocity data we have derived an orbit with a period of 5 years. From this orbit we have derived limits on the mass of the companion (V1334 Cyg C) of 3.1 to 4.4 Msolar. The system is also a marginally resolved visual binary with a much longer period that has been observed for nearly a century. We have used an IUE high-resolution spectrum to conclude that the hottest star in the system (V1334 Cyg B), which dominates the spectrum in the ultraviolet, is the wide companion, since the velocity is very near the systemic velocity.

Binary/multiple status can affect stars at all stages of their lifetimes: evolution onto the main sequence, properties on the main sequence, and subsequent evolution. 5 Msolar stars have provided a wealth of information about the binary properties fairly massive stars. The combination of cool evolved primaries and hot secondaries in Cepheids (geriatric B stars) have yielded detailed information about the distribution of mass ratios. and have also provided a surprisingly high fraction of triple systems. Ground-based radial velocity orbits combined with satellite data from Hubble, FUSE, IUE, and Chandra are needed to provide full information about the systems, including the masses. As a recent example, X-ray observations can identify low mass companions which are young enough to be physical companions. Typically binary status and properties (separation, eccentricity, mass ratio) determine whether any stage of evolution takes an exotic form.

A new orbit has been computed for the binary Cepheid S Mus combining new data from Mount John Observatory with previous data. Corrections to the colors and reddening due to the light from the companion are derived. The spectral type determined from IUE low-dispersion spectra is used for these corrections. The corrections are small, even though the companion is one of the hottest (B5 V) known for a Cepheid.

Infrared astronomy is a natural tool to use in studying star formation because infrared light penetrates the surrounding dust and because protostars are expected to emit infrared light. Infrared mapping and photometry have revealed many compact sources, often embedded in more extensive warm dust associated with a molecular cloud core. More detailed study of these objects is now beginning, and traditional interpretations are being questioned. Some compact sources are now thought to be density enhancements which are not self-luminous. Infrared excesses around young stars may not always be caused by circumstellar dust; speckle measurements have shown that at least some of the excess toward T Tauri is caused by an infrared companion. Spectroscopic studies of the dense, star-forming cores and of the compact objects themselves have uncovered a wealth of new phenomena, including the widespread occurrence of energetic outflows. New discoveries with IRAS and with other planned infrared telescopes will continue to advance this field.

We are carrying out an intensive study of the physical and evolutionary properties of Classical Cepheids, known as the 'Secret Lives of Cepheids' (SLiC) program. This program covers a wide range of periods and pulsation amplitudes, and makes use of X-ray/UV/optical observations. The major science goals of our proposed Spitzer program are to investigate two recently discovered characteristics of Classical Cepheids, hitherto unknown. These are the presence of circumstellar envelopes (CSEs) around three nearby Cepheids (Polaris, delta Cep and L Car - all SLiC program stars), and the existence of O VI (1032/36A) and C III (977A) emission lines in the far-UV spectra of two program stars - Polaris and beta Dor. These lines form in the chromospheres/transition regions of the Cepheids and, in the case of beta Dor, show variations that correlate to the pulsations of the star. We propose SST/IRS high-resolution spectroscopy of these four nearby, bright Classical Cepheids, three of which have been found, from long-baseline near-IR interferometry, to have CSEs ~0.5-3.0 AU from the central star. From the proposed IRS spectra, we will determine the physical characteristics of the circumstellar material/envelopes, likely arising from mass loss or, given the young ages of Cepheids, debris disks. Also, we will use the IRS spectra to explore the presence of emission lines related to those discovered in the far-UV. Possible low density He I and H I wind lines will also be measured, if present. As in the case of the FUSE far-UV observations, SST/IRS also provides the opportunity to observe and measure these emission lines at wavelengths where the Cepheid photospheric continua are very low. In the near-UV to near-IR regions, emission lines are overwhelmed by the photospheric continua. With the modest amount of time requested (~1.86-hours), the proposed IRS observations will be crucial in understanding these newly discovered characteristics of Astronomy's most important and 'best-known' class of variable stars.

We have observed the double cluster h and chi Per with the ROSAT PSPC for 11 ksec. Emission is concentrated toward the two cluster centers, however the resolution at the distance of the clusters (2.4 kpc) is too poor to say whether the emission is diffuse or from a population of unresolved faint sources. 30 sources were found (at the 2.5 sigma level), with an X-ray luminosity of log L = 31.5 ergs sec(-1) or greater. These sources occur in the cluster nuclei, between the clusters and in the halo around the cluster pair. Individual optical sources cannot be identified, but because of the lack of correlation between the X-ray sources and B stars, we conclude that the X-rays are produced by late spectral type pre-main sequence stars. The X-ray sources are brighter than all but the brightest sources in the younger Orion Nebula cluster. These h and chi sources may represent the peak X-ray flux prior to the main sequence when stars have spun up more than the Orion Nobula stars but have still not fully contracted to the main sequence.