Publications of the Astronomical Society of the Pacific

Smith, Graeme H.; Briley, Michael M.

doi: 10.1086/444485pmid: N/A

In this paper, we investigate the behavior of the λ3883 CN absorption bands in the spectra of red giants in the globular cluster Messier 4. Data from three literature sources, including the original survey of Norris, have been combined to produce a picture of the CN band strength over an absolute magnitude range of − 2.5<MV < + 0.5. In addition, measurements of carbon and oxygen abundances, as well as radial velocities, have been compiled from the literature and used to compare the properties of the CN‐strong and CN‐weak groups of giants evident in the cluster. Large CN differences are present among both red giant branch and asymptotic giant branch stars. Although the CN‐weak giants have higher [C/Fe] and [O/Fe] abundances on average than the CN‐strong giants, there is a considerable range in the abundances of both elements among the CN‐strong stars. The radial velocity dispersion of the available sample of CN‐strong stars is identical within the observational errors to that of the CN‐weak stars. A small fraction of cluster giants have CN bands of intermediate strength, and there is a curious trend for these red giants to be concentrated within the inner five core radii of the cluster, although this is still within the uncertainties of small‐sample statistics. The observations are consistent with a hybrid picture for the origin of CNO element inhomogeneities in M4. Deep mixing within stars on the upper red giant branch (MV < - 1.0) is indicated by the relatively low [C/Fe] or [O/Fe] abundances of these giants. However, the large scatter in [C/Fe] and [N/Fe] among fainter stars (at MV≳0) suggests the possibility of a pre‐RGB component to the abundance inhomogeneities. Accretion of material from a central reservoir of stellar ejecta, or mass transfer within binary star systems, are discussed as possible origins for the enrichment of the CN‐strong stars. In the case of M4, these processes must have occurred at sufficiently early times that dynamical relaxation of the cluster has largely erased any initial gradient in the relative space densities of CN‐strong and CN‐weak stars, at least within the volume of the current stellar sample that extends to three half‐mass radii from the cluster center.

King, Jeremy R.; Schuler, Simon C.

doi: 10.1086/432457pmid: N/A

We use new and extant literature spectroscopy to address abundances and membership for UMa moving group stars. We first compare the UMa, Coma, and Hyades H‐R diagrams via a homogeneous set of isochrones and find that these three aggregates are essentially coeval; this (near) coevality can explain the indistinguishable distributions of UMa and Hyades dwarfs in the chromospheric emission versus color plane. Our spectroscopy of cool UMa dwarfs reveals striking abundance anomalies—trends with Teff, ionization state, and excitation potential—like those recently seen in young, cool M34, Pleaides, and Hyades dwarfs. In particular, the trend of rising λ7774‐based O i abundance with declining Teff is markedly subdued in UMa compared to the Pleiades, suggesting a dependence on age or metallicity. Recent photometric metallicity estimates for several UMa dwarfs are markedly low compared to the group’s canonical metallicity, and similar deviants are seen among cool Hyads as well. Our spectroscopy does not confirm these curious photometric estimates, which seem to be called into question for cool dwarfs. Despite disparate sources of Li data, our homogeneous analysis indicates that UMa members evince remarkably small scatter in the Li‐ Teff plane for Teff≥5200 K. Significant star‐to‐star scatter suggested by previous studies is seen for cooler stars. Comparison with the consistently determined Hyades Li‐ Teff trend reveals differences that are qualitatively consistent with this cluster’s larger [Fe/H] (and perhaps slightly greater age). However, quantitative comparison with standard stellar models indicates the differences are smaller than expected, suggesting the action of a fourth parameter beyond age, mass, and [Fe/H] controlling Li depletion. The UMa‐Coma cool star Li abundances may show a slight 0.2 dex difference; however, this may be mass‐independent and thus more consistent with a modest initial Li abundance difference.

Patterson, Joseph; Thorstensen, John R.; Armstrong, Eve; Henden, Arne A.; Hynes, Robert I.

doi: 10.1086/432492pmid: N/A

We report a photometric study of the WZ Sagittae–type dwarf nova PQ Andromedae. The light curve shows strong (0.05 mag full amplitude) signals with periods of 1263(1) and 634(1) s, and a likely double‐humped signal with P = 80.6(2) minutes. We interpret the first two as nonradial pulsation periods of the underlying white dwarf, and the last as the orbital period of the underlying binary. We estimate a distance of 150(50) pc from proper motions and the two standard candles available: the white dwarf and the dwarf‐nova outburst. At this distance, the K magnitude implies that the secondary is probably fainter than any star on the main sequence—indicating a mass below the Kumar limit at 0.075 M⊙. PQ And may be another “period bouncer,” where evolution now drives the binary out to a longer period.

Vanlandingham, Karen M.; Schwarz, Greg J.; Howell, Steve B.

doi: 10.1086/432456pmid: N/A

We have detected pulsations in time‐series photometry of the WZ Sge dwarf nova PQ Andromedae. The strongest peak in the power spectrum occurs at a period of 10.5 minutes. Similar periods have been observed in other WZ Sge systems and are attributed to ZZ Ceti–type nonradial pulsations. There is no indication in the photometry of an approximately 1.7 hr orbital period, as reported in previous spectroscopic observations.

Shafter, Allen W.; Cannizzo, John K.; Waagen, Elizabeth O.

doi: 10.1086/432784pmid: N/A

We examine AAVSO (American Association of Variable Star Observers) light curves of 16 Z Camelopardalis systems with measured orbital periods, with particular focus on intervals away from standstill. During these times, most of the systems display a sawtooth‐like outburst behavior, with quiescent intervals comparable to the outburst durations. We report the discovery of a linear relation between the characteristic outburst period and orbital period for these systems, which is given by 〈Pout(days)〉 = 62.0(± 7.7)Porb(days) + 2.41(± 1.87).

Morgan, G. E.; Ringwald, F. A.; Buil, C.; Garrett, M.

doi: 10.1086/432227pmid: N/A

This paper collects together early IAU Circular observations, plots the light curve, and presents our own spectra of V475 Scuti (Nova Sct 2003). We describe the early spectral evolution of this nova during the 7 weeks after its discovery. The principal spectra show this nova to be a common Fe ii type (R. E. Williams et al.). The nova displayed dominant Balmer lines and numerous Fe ii multiplets (42, 48, 49, 55, and 74), with strong, well‐distributed P Cygni profiles that disappeared near the end of our observations. Spectral evolution produced low‐ionization forbidden lines consistent with an auroral phase (R. E. Williams et al.). V475 Sct was a fast nova, with t2 = 22 days and with a type Ba light curve (H. W. Duerbeck) from the American Association of Variable Star Observers. The Hα velocity widths showed a twofold increase, together with an unusual broadening of the line, during our observations. The lack of structure within the high‐resolution Hα profiles suggests that the nova is exhibiting an isotropic expansion as an optically thick wind, which may result in material falling back onto the white dwarf. We encourage further monitoring.

Schmidtobreick, L.; Galli, L.; Whiting, A.; Tappert, C.; Carver, A. J.

doi: 10.1086/432671pmid: N/A

We present low‐resolution optical spectroscopy for six cataclysmic variable candidates and the old nova V888 Cen. We confirm the classification as cataclysmic variable for LB 9963 and FQ Mon, while the other four candidates turn out to be different types of stars. We discuss the individual spectra and pay special attention to the mass transfer rate and disk temperature and density of the three cataclysmic variables.

Steinfadt, Justin D. R.; Clayton, Geoffrey C.; Evans, Tom Lloyd; Williams, Tom

doi: 10.1086/432848pmid: N/A

We report the first detection of new dust formation in an SC star. The prototype of the SC stars, UY Cen, underwent a decline of 2 mag in the V band. The SC stars show pulsational variations and have 60 μm excesses, indicating past dust formation. It has been suggested that as a star evolves from being oxygen rich to carbon rich, there is a short period of time when C/O ∼ 1 during which the star appears spectroscopically as an SC star and ceases to produce dust. The SC star BH Cru has shown large spectroscopic and pulsation period variations over only 30 yr, indicating rapid evolution, but it has shown no sign of new dust formation. UY Cen has not shown any pulsation or spectroscopic variations accompanying the onset of its dust formation. In addition, UY Cen did not show emission in the resonance lines of Na i, K i, or Rb i when it was at its faintest, although these lines were a feature of the carbon stars R Lep and V Hya during similar faint phases.

Hintz, Eric G.; Rose, Michael B.

doi: 10.1086/432147pmid: N/A

We present photometric and spectroscopic results for two reported δ Scuti stars in the field of NGC 6882/6885. We find that V381 Vul has a period of 0.1185 days and is a δ Scuti variable, as previously reported. The spectra of V382 Vul shows it to be a B3 star and therefore not a δ Scuti. All evidence points to V382 Vul being a β Cephei star with a period of 0.1808 days. Additionally, we report five new variables and eight suspected variable stars. Of the five new variables, two are pulsators and three are eclipsing binary systems. In our search for new variable stars, we use a “robust median statistic” that is proven to be better at finding low‐amplitude variables than the traditional error curve approach.

Turner, David G.; Forbes, Douglas

doi: 10.1086/432025pmid: N/A

Photoelectric UBV photometry is presented for stars in a field closely adjacent to the Wolf‐Rayet star WR 55 (WN7) in a search for a possible parent cluster. There is a group of at least eight stars ∼7′ south‐southeast of the WR star forming a newly discovered, sparsely populated open cluster (designated C1331−622), but the stars are only 819 ± 26 pc distant, less than a quarter of the predicted distance to WR 55.