bluuebunny/crossref_metadata_2025_split huggingface dataset:
The occurrence of non-pulsating stars in the γ Dor and δ Sct instability regions
Authors: Guzik Joyce A. , Bradley Paul A. , Jackiewicz Jason , Uytterhoeven Katrien , Kinemuchi Karen 
Published: February 2014

AbstractWe examine the light curves of over 2700 stars observed in long cadence by the Kepler spacecraft as part of the Guest Observer program. Most of these stars are faint (Kepler magnitude > 14), and fall near or within the effective temperature and log g range of the γ Dor and δ Sct instability strips. We find that the pulsating stars are obvious from inspection of the light curves and power spectra, even for these faint stars. However, we find that a large number of stars are ‘constant’, i.e. show no frequencies in the 0.2 to 24 d−1 range above the 20 ppm level. We discuss the statistics for the constant stars, and some possible physical reasons for lack of pulsations. On the other hand, γ Dor and δ Sct candidates have been found in the Kepler data spread throughout and even outside of the instability regions of both types that were established from pre-Kepler ground-based observations. We revisit mechanisms to produce g- or p-mode pulsations in conditions when these modes are not expected to be unstable via the He-ionization κ effect (δ Sct) or convective blocking (γ Dor) pulsation driving mechanisms.
Interpretation of the oscillation spectrum of HD 50230 — a failure of richness
Authors: Szewczuk Wojciech , Daszyńska-Daszkiewicz Jadwiga , Dziembowski Wojciech 
Published: February 2014

AbstractAttempts to interpret the observed oscillation spectrum of the SPB star HD 50230 are reported. We argue that a nearly equidistant period spacing found in the oscillation spectrum of the star is most likely accidental. The observed period distribution requires excitation of modes with the degree l > 4. Much more may be learned from the rich oscillation spectrum of the star but most of the work is still ahead of us.
A working hypothesis about the cause of Be stars: Episodic outward leakage of low-frequency waves excited by the iron-peak κ-mechanism
Authors: Shibahashi Hiromoto 
Published: February 2014

AbstractObservations indicate that a circumstellar disk is formed around a Be star while the stellar rotation is below the break-up velocity. I propose a working hypothesis to explain this mystery by taking account of the effect of leaky waves upon angular momentum transfer.In B-type stars near the main sequence, low-frequency nonradial oscillations are excited by the κ-mechanism in the iron bump. They transport angular momentum from the driving zone to the surface. As a consequence, the angular momentum is gradually deposited near the stellar surface. This results in a gradual increase in the “critical frequency for g-modes”, and g-modes eventually start to leak outward, long before the surface rotation reaches the break-up velocity. This leads to a substantial amount of angular momentum loss from the star, and a circumstellar disk is formed. The oscillations themselves will be soon damped owing to kinetic energy loss. Then the envelope of the star spins down and angular momentum loss stops soon. The star returns to being quiet and remains calm until nonradial oscillations are newly built up by the κ-mechanism to sufficient amplitude and a new episode begins.According to this view, the interval of episodic Be-star activity corresponds to the growth time of the oscillation, and it seems in good agreement with observations.
Radiative hydrodynamic simulations of turbulent convection and pulsations of Kepler target stars
Authors: Kitiashvili Irina N. 
Published: February 2014

AbstractThe problem of interaction of stellar pulsations with turbulence and radiation in stellar convective envelopes is central to our understanding of excitation mechanisms, oscillation amplitudes and frequency shifts. Realistic (“ab initio”) numerical simulations provide unique insights into the complex physics of pulsation-turbulence-radiation interactions, as well as into the energy transport and dynamics of convection zones, beyond the standard evolutionary theory. 3D radiative hydrodynamics simulations have been performed for several Kepler target stars, from M- to A-class along the main sequence, using a new ‘StellarBox’ code, which takes into account all essential physics and includes subgrid scale turbulence modeling. The results reveal dramatic changes in the convection and pulsation properties among stars of different mass. For relatively massive stars with thin convective envelopes, the simulations allow us to investigate the dynamics the whole envelope convection zone including the overshoot region, and also look at the excitation of internal gravity waves. Physical properties of the turbulent convection and pulsations, and the oscillation spectrum for two of these targets are presented and discussed in this paper. In one of these stars, with mass 1.47 M⊙, we simulate the whole convective zone and investigate the overshoot region at the boundary with the radiative zone.
Pulsation and mass loss across the H-R diagram: From OB stars to Cepheids to red supergiants
Authors: Neilson Hilding R. 
Published: February 2014

AbstractBoth pulsation and mass loss are commonly observed in stars and are important ingredients for understanding stellar evolution and structure, especially for massive stars. There is a growing body of evidence that pulsation can also drive and enhance mass loss in massive stars and that pulsation-driven mass loss is important for stellar evolution. In this review, I will discuss recent advances in understanding pulsation-driven mass loss in massive main-sequence stars, classical Cepheids and red supergiants and present some challenges remaining.
Asteroseismology, standard candles and the Hubble Constant: what is the role of asteroseismology in the era of precision cosmology?
Authors: Neilson Hilding R. , Biesiada Marek , Evans Nancy Remage , Marconi Marcella , Ngeow Chow-Choong , Reese Daniel R. 
Published: February 2014

AbstractClassical Cepheids form one of the foundations of modern cosmology and the extragalactic distance scale; however, cosmic microwave background observations measure cosmological parameters and indirectly the Hubble Constant, H0, to unparalleled precision. The coming decade will provide opportunities to measure H0 to 2% uncertainty thanks to the Gaia satellite, JWST, ELTs and other telescopes using Cepheids and other standard candles. In this work, we discuss the upcoming role for variable stars and asteroseismology in calibrating the distance scale and measuring H0 and what problems exist in understanding these stars that will feed back on these measurements.
Mode selection in pulsating stars
Authors: Smolec Radosław 
Published: February 2014

AbstractIn this review we focus on non-linear phenomena in pulsating stars: mode selection and amplitude limitation. Of many linearly excited modes, only a fraction is detected in pulsating stars. Which of them are excited, and why (the problem of mode selection), and to what amplitude (the problem of amplitude limitation) are intrinsically non-linear and still unsolved problems. Tools for studying these problems are briefly discussed and our understanding of mode selection and amplitude limitation in selected groups of self-excited pulsators is presented. We focus on classical pulsators (Cepheids and RR Lyrae stars) and main-sequence variables (δ Scuti and β Cephei stars). Directions of future studies are briefly discussed.
Pulsations in white dwarf stars
Authors: Fontaine G. , Bergeron P. , Brassard P. , Charpinet S. , Dufour P. , Giammichele N. , Randall S. K. , Van Grootel V. 
Published: February 2014

AbstractWe first present a brief description of the six distinct families of pulsating white dwarfs that are now known. These are all opacity-driven pulsators showing low- to mid-order, low-degree gravity modes. We then discuss some recent highlights that have come up in the field of white dwarf asteroseismology.
The internal structure of ZZ Cet stars using quantitative asteroseismology: The case of R548
Authors: Giammichele N. , Fontaine G. , Brassard P. , Charpinet S. 
Published: February 2014

AbstractWe explore quantitatively the low but sufficient sensitivity of oscillation modes to probe both the core composition and the details of the chemical stratification of pulsating white dwarfs. Until recently, applications of asteroseismic methods to pulsating white dwarfs have been far and few, and have generally suffered from an insufficient exploration of parameter space. To remedy this situation, we apply to white dwarfs the same double-optimization technique that has been used quite successfully in the context of pulsating hot B subdwarfs. Based on the frequency spectrum of the pulsating white dwarf R548, we are able to unravel in a robust way the unique onion-like stratification and the chemical composition of the star. Independent confirmations from both spectroscopic analyses and detailed evolutionary calculations including diffusion provide crucial consistency checks and add to the credibility of the inferred seismic model. More importantly, these results boost our confidence in the reliability of the forward method for sounding white dwarf internal structure with asteroseismology.
Sunquakes and starquakes
Authors: Kosovichev Alexander G. 
Published: February 2014

AbstractIn addition to well-known mechanisms of excitation of solar and stellar oscillations by turbulent convection and instabilities, the oscillations can be excited by an impulsive localized force caused by the energy release in solar and stellar flares. Such oscillations have been observed on the Sun (‘sunquakes’), and created a lot of interesting discussions about physical mechanisms of the impulsive excitation and their relationship to the flare physics. The observation and theory have shown that most of a sunquake's energy is released in high-degree, high-frequency p modes. In addition, there have been reports on helioseismic observations of low-degree modes excited by strong solar flares. Much more powerful flares observed on other stars can cause ‘starquakes’ of substantially higher amplitude. Observations of such oscillations can provide new asteroseismic information and also constraints on mechanisms of stellar flares. I discuss the basic properties of sunquakes, and initial attempts to detect flare-excited oscillations in Kepler short-cadence data.
g-mode trapping and period spacings in hot B subdwarf stars
Authors: Charpinet S. , Van Grootel V. , Brassard P. , Fontaine G. 
Published: February 2014

AbstractHot B subdwarfs (sdB) are hot and compact helium core burning stars of nearly half a solar mass that can develop pulsational instabilities driving acoustic and/or gravity modes. These evolved stars are expected to be chemically stratified with an almost pure hydrogen envelope surrounding a helium mantle on top of a carbon/oxygen enriched core. However, the sdB stars pulsating in g-modes show regularities in their observed period distributions that, surprisingly (at first sight), are typical of the behavior of high order g-modes in chemically homogeneous (i.e., non-stratified) stars. This led to a claim that hot B subdwarfs could be much less chemically stratified than previously thought. Here, we reinvestigate trapping effects affecting g-modes in sdB stars. We show that standard stratified models of such stars can also produce nearly constant period spacings in the low frequency range similar to those found in g-mode spectra of sdB stars monitored with Kepler.
The mean density and the surface gravity of the primary component of μ Eridani, an SPB variable in a single-lined spectroscopic and eclipsing system
Authors: Jerzykiewicz Mikołaj 
Published: February 2014

AbstractPrecision asteroseismology uses the observed effective temperature and luminosity or surface gravity in selecting evolutionary models for analysis. In the case of the primary component of μ Eri, an SPB variable, the surface gravity and luminosity can be derived from the parameters of the SB1 eclipsing system. We examine how the surface gravity and luminosity so derived help to select the evolutionary models suitable for asteroseismic analysis.
Revision of the [Fe/H] – φ31–Prelationship for RRc variables
Authors: Morgan Siobahn 
Published: February 2014

AbstractThe relationship derived by Morganet al. (2007) for type-c RR Lyrae variables (RRc) between values of [Fe/H] – φ31–Phas been revised and expanded. New relationships are based upon Fourier coefficients of 163 RRc variables in 19 Galactic globular clusters using the metallicity scales of Harris (2010), Zinn & West (1984) and Carrettaet al. (2009). This larger database includes more low-metallicity clusters ([Fe/H] < −2.0), and the best fitting relations are found to depend upon values of logPrather thanP. The new relations are applied to various populations of RRc including Milky Way field variables, LMC globular clusters variables, ω Cen RRc, and RRc in various OGLE III databases.
Variable stars in open clusters
Authors: Paunzen E. , Zejda M. , Mikulášek Z. , Liška J. , Krtička J. , Janík J. , Netopil M. , Fossati L. , Baumann B. 
Published: February 2014

AbstractWe present our joint efforts to study variable stars in open clusters. This includes a new catalogue, a photometric survey for new variables, and the database WEBDA. Our tools will shed more light on stellar variability in open clusters.
Global Astrophysical Telescope System – GATS
Authors: Polińska M. , Kamiński K. , Dimitrov W. , Fagas M. , Borczyk W. , Kwiatkowski T. , Baranowski R. , Bartczak P. , Schwarzenberg–Czerny A. 
Published: February 2014

AbstractThe Global Astronomical Telescope System is a project managed by the Astronomical Observatory Institute of Adam Mickiewicz University in Poznań (Poland) and it is primarily intended for stellar medium/high resolution spectroscopy. The system will be operating as a global network of robotic telescopes. The GATS consists of two telescopes: PST 1 in Poland (near Poznań) and PST 2 in the USA (Arizona). The GATS project is also intended to cooperate with the BRITE satellites and supplement their photometry with spectroscopic observations.
The BlaSGalF database
Authors: Skarka Marek 
Published: February 2014

AbstractBlaSGalF is the name of an online, regularly updated list of known RR Lyraes exhibiting the Blazhko effect. It is an acronym of Blazhko Stars of Galactic Field. The list currently contains about 270 stars. It gives basic information about positions, brightnesses, pulsation and modulation periods based on data from catalogs and more than sixty papers. Using this database we found a lack of Blazhko stars with appropriate period characteristics. We introduce the present form of the list and discuss future plans for this database.
Variable stars in the field of the young open cluster Roslund 2
Authors: Sowicka P. , Handler G. , Taubner R. , Brunner M. , Passegger V.-M. , Bauer F. , Paunzen E. 
Published: February 2014

AbstractThe study of variable stars in open clusters via asteroseismology is a powerful tool for the study of stellar evolution and stars in general. That is because stars in clusters can be assumed to originate from the same interstellar cloud, so they share similar properties such as age and overall metallicity. We performed a search for variable stars in the field of the young open star cluster Roslund 2, with photoelectric and CCD photometry acquired at two different telescopes. Within the resulting light curves we have found 12 variable stars. Our measurements confirm three previously known variables.
Oscillation parameters of red giants observed in the CoRoT exofield
Authors: Themessl N. , Kallinger T. , Montalbán J. , García R. A. 
Published: February 2014

AbstractThe high-precision data obtained by the CoRoT (Convection, Rotation and planetary Transits) space mission allows firm detections of solar-like oscillations in a great variety of different stars. We derived reliable estimates of the frequency of maximum oscillation power νmax and the large frequency separation Δν of more than 300 cool red giants, that were observed by CoRoT. A detailed study of their seismic parameters provides an exclusive view of the population of the observed giants.
Anomalously Broad Diffuse Interstellar Bands and Excited CH+ Absorption in the Spectrum of Herschel 36
Authors: York D. G. , Dahlstrom J. , Welty D. E. , Oka T. , Hobbs L. M. , Johnson S. , Friedman S. D. , Jiang Z. , Rachford B. L. , Snow T. P. , Sherman R. , Sonnentrucker P. 
Published: February 2014

AbstractAnomalously broad diffuse interstellar bands (DIBs) at 5780.5, 5797.1, 6196.0, and 6613.6 Å are found in absorption along the line of sight to Herschel 36, an O star system next to the bright Hourglass nebula of the Hii region Messier 8. Excited lines of CH and CH+ are seen as well. We show that the region is very compact and itemize other anomalies of the gas. An infrared-bright star within 400 AU is noted. The combination of these effects produces anomalous DIBs, interpreted by Oka et al. (2013, see also this volume) as being caused predominantly by infrared pumping of rotational levels of relatively small molecules.
Analysis of Anomalous Diffuse Interstellar Bands in the Spectrum of Herschel 36
Authors: Oka T. , Welty D. E. , Johnson S. , York D. G. , Dahlstrom J. , Hobbs L. M. 
Published: February 2014

AbstractThe extraordinary DIBs observed toward Herschel 36 (Dahlstrom et al. 2013) have been analyzed (Oka et al. 2013). The analysis led us to a new way to classify the carriers of DIBs depending on whether the molecules are polar or non-polar. The pronounced Extended Tails toward Red (ETR) observed for DIBs λ5780.5, λ5797.1, and λ6613.6 are explained as due to radiative excitation of high rotational levels of polar carrier molecules in an environment with high radiative temperature ~90 K. Other DIBs (e.g., λ5849.8, λ6196.0, and λ6379.3) which do not show ETR are likely due to non-polar molecules. Model calculations taking into account the interplay of radiative and collisional effects reproduce the observed ETR using realistic molecular parameters if the radiative temperature is sufficiently high (~90 K). The calculation suggests that the carriers of DIBs with ETR are likely medium size molecules with 3 - 6 heavy atoms unless the radiative temperature is much higher.
Towards Extraction of Massive DIB Datasets from Stellar Spectroscopic Surveys
Authors: Lallement R. , Chen H.C , Puspitarini L. , Bonifacio P. , Babusiaux C. , Hill V. 
Published: February 2014

AbstractMedium to high-resolution stellar spectroscopic surveys can potentially be used to build DIB databases by means of automated methods of analysis. Multiplex spectrographs increase strongly those potentialities and allow small-scale variability studies. Because measurements of the stellar parameters are generally the primary goal of the surveys, synthetic spectra can be computed and used to extract DIBs from late-type star data. Large datasets should allow deeper investigations on the DIB variability in response to stellar radiation fields, DIB reddening relationships, and help localizing interstellar clouds. Here we describe our attempts to build and test automated methods adapted to both early and late type stars.
DIBs Broadening with Increased Abundance of Vibrationally Excited H2 Molecules
Authors: Gnaciński P. , Krełowski J. 
Published: February 2014

AbstractThe analysis of DIB profiles was used in various attempts to discover the DIBs carriers. The broadening of the 6196 Å DIB with increasing C2 rotational temperature was reported by Kaźmierczak et al. (2009). We present the broadening of the 4763, 5780 and 6614 Å DIBs connected with higher abundance of vibrationally excited hydrogen molecule. The DIBs broadening is also correlated with increasing H2 rotational temperature on the ν=2 vibrational level. The broadening may be caused by growing population of higher rotational levels in the DIB carrier. Some DIBs, like 4964 Å, do not show any width changes with higher population of vibrationally excited H2.
Search for DIBs in Emission: MWC 922 - The Red Square Nebula
Authors: Wehres N. , Ochsendorf B. , Bally J. , Snow T , Bierbaum V. , Cox N. L. J. , Kaper L. , Tielens A. G. G. M. 
Published: February 2014

AbstractThis work focusses on MWC 922, the central object in the Red Square Nebula. We obtained low and medium resolution spectra of both, the central object and the surrounding nebula, using the DIS and TSpec spectrograph. The spectra show the whole spectral range between ~3 500 Å up to ~25 000 Å. The central object shows a plethora of emission lines, including many Fe II and forbidden Fe [II] lines. Here, we present the inventory of the emission lines of the central object, MWC 922. Future work will comprise the identification of the nebula emission lines by using newly obtained X-Shooter spectra. That way we want to gain further insight into the physical and chemical conditions in this environment. A comparison of the Red Square to the Red Rectangle Nebula is anticipated and will guide our search for DIBs in emission.
Laboratory Studies of Ion Chemistry in the Interstellar Medium
Authors: Bierbaum V. M. 
Published: February 2014

AbstractStudies of gas phase ion-neutral reactions provide insight into many areas of astrochemistry, including the elusive characterization of the Diffuse Interstellar Bands (DIBs). This presentation gives an overview of our experimental studies of several classes of positive and negative ions, using the flowing afterglow-selected ion flow tube and a newly modified ion trap. Earlier studies of carbon chain anions and polycyclic aromatic hydrocarbon (PAH) cations, both of which have been suggested as carriers of the DIBs, are described. More recent work including isomeric PAHs, nitrogen-containing PAHs, negative ions of PAHs, and negative ions of 5-membered heterocyclic rings are discussed. Finally, the study of quantitative thermochemistry by coupling our results with data from Photoelectron Spectroscopy is described.
The increase in BIK expression following ERK1/2 pathway inhibition is a consequence of G1 cell-cycle arrest and not a direct effect on BIK protein stability
Authors: Sale Matthew J. , Cook Simon J. 
Published: February 2014

BIK (BCL2-interacting killer) is a pro-apoptotic BH3 (BCL2 homology domain 3)-only protein and a member of the BCL2 protein family. It was proposed recently that BIK abundance is controlled by ERK1/2 (extracellular-signal-regulated kinase 1/2)-catalysed phosphorylation, which targets the protein for proteasome-dependent destruction. In the present study, we examined ERK1/2-dependent regulation of BIK, drawing comparisons with BIMEL (BCL2-interacting mediator of cell death; extra long), a well-known target of ERK1/2. In many ERK1/2-dependent tumour cell lines, inhibition of BRAFV600E (v-raf murine sarcoma viral oncogene homologue B1, V600E mutation) or MEK1/2 (mitogen-activated protein kinase/ERK kinase 1/2) had very little effect on BIK expression, whereas BIMEL was strongly up-regulated. In some cell lines we observed a modest increase in BIK expression; however, this was not apparent until ~16 h or later, whereas BIMEL expression increased rapidly within a few hours. Although BIK was degraded by the proteasome, we found no evidence that this was regulated by ERK1/2 signalling. Rather, the delayed increase in BIK expression was prevented by actinomycin D, and was accompanied by increases in BIK mRNA. Finally, the delayed increase in BIK expression following ERK1/2 inhibition was phenocopied by a highly selective CDK4/6 (cyclin-dependent kinases 4 and 6) inhibitor, which caused a strong G1 cell-cycle arrest without inhibiting ERK1/2 signalling. In contrast, BIMEL expression was induced by ERK1/2 inhibition, but not by CDK4/6 inhibition. We conclude that BIK expression is not subject to direct regulation by the ERK1/2 pathway; rather, we propose that BIK expression is cell-cycle-dependent and increases as a consequence of the G1 cell-cycle arrest which results from inhibition of ERK1/2 signalling.