Phenomena In Stars Research Articles

Time-dependent extension of the self-consistent band theory for neutron star matter: Anti-entrainment effects in the slab phase

Background: In the solid crust of neutron stars, a variety of crystalline structure may exist. Recently the band theory of solids has been applied to the inner crust of neutron stars and significance of the entrainment between dripped neutrons and the solid crust was advocated. Since it influences interpretations of various phenomena of neutron stars, it has been desired to develop deeper understanding of the microphysics behind. Purpose: The purpose of the present article is to propose a fully self-consistent microscopic framework for describing time-dependent dynamics of neutron star matter, which allows us to explore diverse properties of nuclear matter, including the entrainment effect. Results: As the first application of the time-dependent self-consistent band theory for nuclear systems, we investigate the slab phase of nuclear matter with various proton fractions. From a dynamic response of the system to an external force, we extract the collective mass of a slab, associated with entrained neutrons as well as bound nucleons. We find that the extracted collective mass is smaller than a naive estimation based on a potential profile and single-particle energies. We show that the reduction is mainly caused by "counterflow" of dripped neutrons towards the direction opposite to the motion of the slabs. We interpret it as an "anti-entrainment" effect. As a result, the number of effectively bound neutrons is reduced, indicating an enhancement of the number density of conduction neutrons. We demonstrate that those findings are consistent with a static treatment in the band theory of solids. *shortened due to the arXiv's word limit.

The child prodigy as a global celebrity: the chess wonder Samuel Reshevsky

ABSTRACT Focusing on the chess prodigy Samuel Reshevsky (1911–1992), this paper examines the international commercial exploitation of child prodigies and their rise to celebrity. In the early 1920s, this boy wonder toured Europe and the United States, where he defeated some of the best players in simultaneous chess exhibitions, met important personalities and became a subject of global fascination. His ascent into stardom just before Hollywood’s child star era reveals the public’s eagerness to capitalise on gifted children as yet another commodity of the entertainment industry. Parents played a key role in exploiting child prodigies, despite the success of recent campaigns to secure children’s rights such as compulsory education and the regulation of child labour. Meanwhile, philanthropists attempted to aid children like Reshevsky and stop their public exhibition. Moreover, psychologists examined their talent and worried about their futures. Overall, Reshevsky’s case reconstructs the network of interests (commercial, humanitarian, scientific) surrounding child prodigies and historicises the child star phenomenon beyond the mainstream child performer.

Neutron stars in scalar-tensor theories: Analytic scalar charges and universal relations

Neutron stars are ideal astrophysical sources to probe general relativity due to their large compactnesses and strong gravitational fields. For example, binary pulsar and gravitational wave observations have placed stringent bounds on certain scalar-tensor theories in which a massless scalar field is coupled to the metric through matter. A remarkable phenomenon of neutron stars in such scalar-tensor theories is spontaneous scalarization, where a normalized scalar charge remains order unity even if the matter-scalar coupling vanishes asymptotically far from the neutron star. While most works on scalarization of neutron stars focus on numerical analysis, this paper aims to derive accurate scalar charges analytically. To achieve this, we consider a simple energy density profile of the Tolman VII form and work in a weak-field expansion. We solve the modified Tolman-Oppenheimer-Volkoff equations order by order and apply Pad\'e resummation to account for higher-order effects. We find that our analytic scalar charges in terms of the stellar compactness beautifully model those computed numerically. We also find a quasi-universal relation between the scalar charge and stellar binding energy that is insensitive to the underlying equations of state. Comparison of analytic scalar charges for Tolman VII and constant density stars mathematically support this quasi-universal relation. The analytic results found here provide physically motivated, ready-to-use accurate expressions for scalar charges.

Neutron Tunneling: A New Mechanism to Power Explosive Phenomena in Neutron Stars, Magnetars, and Neutron Star Mergers

Abstract Neutron tunneling between neutron-rich nuclei in inhomogeneous dense matter encountered in neutron star crusts can release enormous energy on a short timescale to power explosive phenomena in neutron stars. In this work, we clarify aspects of this process that can occur in the outer regions of neutron stars when oscillations or cataclysmic events increase the ambient density. We use a time-dependent Hartree–Fock–Bogoliubov formalism to determine the rate of neutron diffusion and find that large amounts of energy can be released rapidly. The roles of nuclear binding, two-body interaction, and pairing in neutron diffusion times are investigated. We consider a one-dimensional quantum diffusion model and extend our analysis to study the impact of diffusion in three dimensions. We find that these novel neutron transfer reactions can generate energy in the amount of ≃ 1040–1044 erg under suitable conditions and assumptions.

STAR AND POOR FUND PHENOMENA IN ISLAMIC- AND CONVENTIONAL-FOCUSED FAMILIES: EMERGING COUNTRY EVIDENCE

The aim of this study is to investigate star and poor phenomena and their impact on the flows of Islamic-focused family (IFF) and conventional-focused family (CFF). The sample includes the four emerging countries with the largest number of Islamic mutual funds from 2007 to 2018 (Saudi Arabia, Malaysia, Indonesia, and Pakistan). Panel regression analysis was used to examine the impact of dummy star and poor as independent variables, and family age, size, number of funds, past returns, and total risk as control variables for fund family flows. The results show that the dummy star has a significantly positive relationship with family flows. Family managers have succeeded in attracting more investors by using the strategy of advertising the best performing funds. However, in both, all families and IFF, the dummy poor has a negative relationship, but is insignificant. On the other hand, for CFFs, the dummy poor is significantly negative. This is because investors in IFFs, unlike those in CFFs, have more loyalty due to their moral and religious goals in addition to traditional goals. The novel finding of the study is the difference in the star phenomenon between the IFF and CFF. The findings are important for managers, as they will help them to create appropriate strategies to attract more flows and increase the assets under their management. In addition, the findings will help investors to direct their money to appropriate families.

Attention Economics of Instagram Stars: #Instafame and Sex Sells?

Social media stars create stardom with uploads on social media pages like YouTube, TikTok or Instagram. One of the most popular platforms, especially designed to upload picture contents, is the service “Instagram” owned by Facebook. The growing social, cultural and economic power of social media star phenomenon raises the question about key drivers of success. Does body exposure drive Instagram success? Is there a difference between male and female content in this regard? This paper empirically analyses 500 top Instagram stars within the categories (1) fashion and beauty, (2) fitness and sports, (3) music, (4) photo and arts, (5) food and vegan. The unbalanced panel data set consists of 100 stars within each category over an observation period of five months. The data provides information on popularity measurements, such as subscribers, likes and comments, and most importantly, price estimates per post. Since influencers are not paid by the platform, but mainly by advertisers for promotion of their products, the estimated price per upload combined with the posting frequency serve as a valid proxy for weekly revenue and economic success. Mean comparison tests show that accounts with focus on female accounts have a significantly higher degree in body exposure, while the price per picture is higher for male content. Weekly revenues do not significantly diverge. Furthermore, using panel regressions, I estimate the effect of body exposure and sex on advertising revenue. The results show that body exposure has a positive effect, whereas the sex has no significant influence in the regression estimations. Eventually, this raises the question of a gender pay gap in social media.

(Sub)stellar companions shape the winds of evolved stars.

Binary interactions dominate the evolution of massive stars, but their role is less clear for low- and intermediate-mass stars. The evolution of a spherical wind from an asymptotic giant branch (AGB) star into a nonspherical planetary nebula (PN) could be due to binary interactions. We observed a sample of AGB stars with the Atacama Large Millimeter/submillimeter Array (ALMA) and found that their winds exhibit distinct nonspherical geometries with morphological similarities to planetary nebulae (PNe). We infer that the same physics shapes both AGB winds and PNe; additionally, the morphology and AGB mass-loss rate are correlated. These characteristics can be explained by binary interaction. We propose an evolutionary scenario for AGB morphologies that is consistent with observed phenomena in AGB stars and PNe.

A plague of magnetic spots among the hot stars of globular clusters

Six decades and counting, the formation of hot ~20,000-30,000 K Extreme Horizontal Branch (EHB) stars in Galactic Globular Clusters remains one of the most elusive quests in stellar evolutionary theory. Here we report on two discoveries shattering their currently alleged stable luminosity. The first EHB variability is periodic and cannot be ascribed to binary evolution nor pulsation. Instead, we here attribute it to the presence of magnetic spots: superficial chemical inhomogeneities whose projected rotation induces the variability. The second EHB variability is aperiodic and manifests itself on time-scales of years. In two cases, the six-year light curves display superflare events a mammoth several million times more energetic than solar analogs. We advocate a scenario where the two spectacular EHB variability phenomena are different manifestations of diffuse, dynamo-generated, weak magnetic fields. Ubiquitous magnetic fields, therefore, force an admittance into the intricate matrix governing the formation of all EHBs, and traverse to their Galactic field counterparts. The bigger picture is one where our conclusions bridge similar variability/magnetism phenomena in all radiative-enveloped stars: young main-sequence stars, old EHBs and defunct white dwarfs.

Stars in social media: new light through old windows?

ABSTRACT We review the economics of superstars, originally developed for stars in traditional media, and discuss whether they are applicable for the novel phenomenon of stars in social media (influencer, micro-celebrities). Moreover, we analyse potentially new factors for creating social media superstardom. Our overall result is that the economics of superstars remain applicable and relevant for social media stars. In line with this assessment, we find that several (allegedly) new star factors in social media, like disappearance of gatekeepers and authenticity, turn out to be just slightly different to traditional concepts. However, algorithm management and upload strategies represent novel success factors relevant for social media superstardom that are not captured by traditional superstar theories.

Amphiphilic miktoarm star copolymers can self-assemble into micelle-like aggregates in nonselective solvents: a case study of polyoxometalate based miktoarm stars

It is well-known that amphiphilic star-shaped copolymers can self-assemble in selective solvents to form complicated micellar constructs as a synergistic result of both the topological constraints and relative volume fractions of the arms. Although the association phenomena of amphiphilic stars have been observed in nonselective solvents, both the structural detail and formation mechanism of these associates are not clear yet. Moreover, these experimental observations are controversial with respect to molecularly dispersed starlike copolymers in nonselective solvents as is popularly believed. To clarify these issues, we have synthesized a series of polyoxometalate-based polystyrene-poly(ethylene glycol) (PS-PEG) miktoarm star supramolecular copolymers (SEW-1-5) by coupling a Keggin-type polyoxometalate of K4[α-SiW12O40] with 1,2,3-triazolium bridged block copolymers of PSn-b+-PEGmI− (n=17, 26, 39, 57, 81; m=45) through ionic exchange reactions, respectively. TEM imaging, contact angle and 1H NMR studies reveal that SEW-2-5 self-assemble in chloroform, THF, and toluene to create micellelike aggregates ranging from cylinder to sphere with a PS corona and a PEG core, while for SEW-1, reverse bilayers are captured with a PEG corona and a PS core. Among these aggregates, the Keggin clusters of [α-SiW12O40]4− localize at the core-corona interfaces between PS and PEG. In terms of solvent quality, chloroform, THF, and toluene are only slightly poorer for PEG than that for PS with a relative order of chloroform<THF<toluene. These unexpected aggregates originate from the topological constraints of the chemically different arms of PS and PEG in the miktoarm stars, where the weak incompatibility between the PS and PEG arms is intensified appropriately. The presence of the reverse bilayered structures of SEW-1 is due to the magnified steric hindrance of the PEG45 arm with decreasing the molecular weight of the PS17 arm. However, to the best of our knowledge, these are the first examples clearly indicating that miktoarm star copolymers can self-assemble in common good solvents or slightly selective solvents to generate micellelike aggregates. This scenario is not only in sharp contrast to the intuitively considered behavior of unimolecular miktoarm stars in nonselective solvents, but also rather different from the conventional self-assembly behavior of amphiphilic star copolymers in selective solvents.

Entrainment effects in neutron-proton mixtures within the nuclear energy-density functional theory: Low-temperature limit

Mutual entrainment effects in cold neutron-proton mixtures are studied in the framework of the self-consistent nuclear energy-density functional theory. Exact expressions for the mass currents, valid for both homogeneous and inhomogeneous systems, are directly derived from the time-dependent Hartree-Fock equations with no further approximation. The equivalence with the Fermi-liquid expression is also demonstrated. Focusing on neutron-star cores, a convenient and simple analytical formulation of the entrainment matrix in terms of the isovector effective mass is found, thus allowing to relate entrainment phenomena in neutron stars to isovector giant dipole resonances in finite nuclei. Results obtained with different functionals are presented. These include the Brussels-Montreal functionals, for which unified equations of state of neutron stars have been recently calculated.

Stellar activity and rotation of the planet host Kepler-17 from long-term space-borne photometry

Context. The study of young Sun-like stars is fundamental to understanding the magnetic activity and rotational evolution of the Sun. Space-borne photometry by the Kepler telescope provides unprecedented datasets to investigate these phenomena in Sun-like stars. Aims. We present a new analysis of the entire Kepler photometric time series of the moderately young Sun-like star Kepler-17 accompanied by a transiting hot Jupiter. Methods. We applied a maximum-entropy spot model to the long-cadence out-of-transit photometry of the target to derive maps of the starspot filling factor versus the longitude and the time. These maps are compared to the spots occulted during transits to validate our reconstruction and derive information on the latitudes of the starspots. Results. We find two main active longitudes on the photosphere of Kepler-17, one of which has a lifetime of at least ∼1400 days although with a varying level of activity. The latitudinal differential rotation is of solar type, that is, with the equator rotating faster than the poles. We estimate a minimum relative amplitude ΔΩ/Ω between ∼0.08 ± 0.05 and 0.14 ± 0.05, our determination being affected by the finite lifetime of individual starspots and depending on the adopted spot model parameters. We find marginal evidence of a short-term intermittent activity cycle of ∼48 days and an indication of a longer cycle of 400−600 days characterized by an equatorward migration of the mean latitude of the spots as in the Sun. The rotation of Kepler-17 is likely to be significantly affected by the tides raised by its massive close-by planet. Conclusion. We confirm the reliability of maximum-entropy spot models to map starspots in young active stars and characterize the activity and differential rotation of this young Sun-like planetary host.

Stars in Social Media: New Light Through Old Windows?

We review the economics of superstars, originally developed for stars in traditional media, and discuss whether they are applicable for the (allegedly) novel phenomenon of stars in social media (influencer, micro-celebrities). Moreover, we analyse potentially new factors for creating social media superstardom that may be special to the nature of social media. Our overall result is that the economics of superstars, like the role of talent, market concentration effects, MacDonald-style and Adler-style effects, remain applicable and relevant for social media stars. In line with this assessment, we find that several (allegedly) new star factors in social media, like user-generated content, prosumption, disappearance of gatekeepers and authenticity, turn out to be only partly applicable or just slightly different to traditional concepts. However, algorithm management and upload strategies represent novel success factors relevant for social media superstardom that are not captured by traditional superstar theories.

National Socialism and German Discourse: Unquiet Voices by W. J. Dodd

 Reviews life and work. Subsequent chapters document the public relations efforts surrounding Hitler’s appearances at film premieres, his representation in wartime newsreels, and his extensive socializing with celebrities at official functions and society events. Niven rightly highlights the difference between the pre-war and war years. Not only did Hitler become closely involved in the approval process for wartime newsreels and anti-Semitic films such as Jew Süss () and e Eternal Jew (); together with Goebbels, he also created the List of the Divinely Gied that protected film professionals from being sent to the front. Significantly, Hitler’s growing need for shaping the image of Nazi Germany for posterity coincided with concerted efforts to minimize his own film appearances—and conceal his Parkinson’s disease. For scholars of German cinema and media and historians working on the ird Reich, this book does not offer much new information or interpretation. Niven does not engage with the existing scholarship, whether on film propaganda (i.e. newsreels , state-commissioned films) or the kind of mainstream cinema that has inspired numerous studies on studio histories, film genres, and the star phenomenon. As a result, opportunities for deeper engagement are missed: how the kind of top-down approach chosen by Niven complicates our understanding of cinema and ideology, or how the focus on Hitler changes our view of the filmic legacies of the Nazi past beyond the familiar complaints about normalization and commercialization and the implicit assumptions about the right and wrong ways of Vergangenheitsbewältigung . Numerous books (none of which is included in the bibliography) have dealt with these questions, from Eric Rentschler’s e Ministry of Illusion: Nazi Cinema and its Aerlife (Cambridge, MA, and London: Harvard University Press, ) to Gavril Rosenfeld’s Hi Hitler! How the Nazi Past Is Normalized in Contemporary Culture (Cambridge: Cambridge University Press, ) to my own Screen Nazis: Cinema, History, and Democracy (Lincoln: Nebraska University Press, ). Niven’s closing assertion that ‘Hitler stood at the very heart of the world in which all actors and directors had moved during the ird Reich’ (p. ) may be true for the small world of film professionals, cultural bureaucrats, and party ideologues. Other scholars have made similar arguments about Goebbels. However, the focus on powerful men leaves unaddressed the competing political, economic, and artistic interests that in the end proved at least as important to the process of film-making in its various stages and components. A minor point: for anyone familiar with the films discussed, the exclusive use of English translations for German titles can be frustrating. U  T  A S H National Socialism and German Discourse: Unquiet Voices. By W. J. D. Cham: Palgrave Macmillan. . x+ pp. £. ISBN ––––. is is a book that does not shout its achievements from the rooops. Addressed to and founded in the practice of linguistic analysis as a corrective to hegemonic discourse, National Socialism and German Discourse is as measured, nuanced, and MLR, .,   deliberative in its explicit treatment of its concerns as it is forcefully eloquent in its implicit application of the same. ematically, the study offers a discourse history of National Socialism read through the private and public counter-discourses of the ‘unquiet voices’, as those German-speaking dissenters against the regime are referred to who, whether marginalized abroad or at home, ‘found themselves in a kind of exile from their speech community’ (p. ). e book’s front-cover image has programmatic value for its structural and analytical thrust. Depicting the architrave of the Reichstag—formerly home to the Imperial Diet, now the seat of the German federal parliament—its focus is on the building’s contentiously worded dedication to the German people: ‘Dem deutschen Volke’. ough fraught with ideological loading in a post- perspective, the inscription itself dates back to , but at the same time it therefore acts as a reminder that National Socialist ideology and terminology did not arise in a vacuum , and it endures as a visible remainder of the past in the present. Yet, as W. J. Dodd argues in the body of the book, since  the Reichstag courtyard has also been inscribed with a counterpoint to the original...

Hitler and Film: The Führer’s Hidden Passion by Bill Niven

MLR, .,   have started a little more from that pole. is feature enables great writing always to be in two places at the same time. R I A H R Hitler and Film: e Führer’s Hidden Passion. By B N. New Haven and London: Yale University Press. . xi+ pp. £.. ISBN ––– –. Written by Bill Niven, a British historian known for his research on Germany’s dif- ficult past, Hitler and Film is part of a growing trend at university presses to publish books aimed at a general readership. Like Ben Urwand’s e Collaboration: Hollywood ’s Pact with Hitler (Berkeley and Los Angeles: Harvard University Press, ), this most recent contribution feeds the unending fascination with Nazi cinema as both the ultimate other of classical Hollywood and the most extreme example of the politicization of film. Aer years of ideology critical studies, film theoretical analyses, and Cultural Studies readings, both books also contribute to a renewed interest in the role of individuals, whether studio bosses or Fascist dictators, in controlling all aspects of film production and reception. Hitler and Film will be a satisfying read for history buffs and film fans interested in the ird Reich. e book is written in a fluid, highly readable style and provides a vivid account of the personal and political ambitions that propelled Hitler to take an intense interest in film as a technology of mass entertainment and a form of political indoctrination. ere are many details involving Hitler’s film-viewing habits, his heated arguments with Goebbels over films in production, and his alternately obsequious and menacing behaviour towards film actresses. Aside from drawing extensively on archival sources from the Bundesarchiv, Niven makes effective use of the numerous memoirs written by Ufa stars trying to justify their professional choices and to profit from the widespread fascination with what is oen described as the first media dictatorship. Hitler’s comments about individual films (e.g. ‘good’, ‘bad’) reveal him as an ardent film fan—but one with surprisingly ordinary tastes and limited powers of discernment. His interventions in ongoing film productions and his interactions with celebrities requesting special treatment confirm the conclusion reached by countless biographies of Hitler, namely, that the Führer enjoyed exercising control over all things major and minor. However, in what ways his decisions shaped a national film culture defined as much by its hierarchical power structure and ideological objectives as by the opportunism, pragmatism, and mediocrity of those working under these conditions remains an open question. Niven introduces the main story of his book by reconstructing Hitler’s intense love of film through the daily screenings at the Berghof and his repeated clashes with Propaganda Minister Joseph Goebbels. e chapters on Leni Riefenstahl, from her first party rally films to Triumph of the Will () and Olympia (), cover familiar ground explored in numerous monographs on (or by) Riefenstahl on her  Reviews life and work. Subsequent chapters document the public relations efforts surrounding Hitler’s appearances at film premieres, his representation in wartime newsreels, and his extensive socializing with celebrities at official functions and society events. Niven rightly highlights the difference between the pre-war and war years. Not only did Hitler become closely involved in the approval process for wartime newsreels and anti-Semitic films such as Jew Süss () and e Eternal Jew (); together with Goebbels, he also created the List of the Divinely Gied that protected film professionals from being sent to the front. Significantly, Hitler’s growing need for shaping the image of Nazi Germany for posterity coincided with concerted efforts to minimize his own film appearances—and conceal his Parkinson’s disease. For scholars of German cinema and media and historians working on the ird Reich, this book does not offer much new information or interpretation. Niven does not engage with the existing scholarship, whether on film propaganda (i.e. newsreels , state-commissioned films) or the kind of mainstream cinema that has inspired numerous studies on studio histories, film genres, and the star phenomenon. As a result, opportunities for deeper engagement are missed: how the kind of top-down approach chosen by Niven complicates...

Glitching Pulsars: Unraveling the Interactions of General Relativistic and Quantum Fields in the Strong Field Regimes

We present a modification of our previous model for the mechanisms underlying the glitch phenomena in pulsars and young neutron stars. Accordingly, pulsars are born with embryonic cores comprising of purely incompressible superconducting gluon-quark superfluid (henceforth SuSu-cores). As the ambient medium cools and spins down due to emission of magnetic dipole radiation, the mass and size of SuSu-cores are set to grow discretely with time, in accordance with the Onsager-Feynmann analysis of superfluidity. Presently, we propose that the spacetime embedding glitching pulsars is dynamical and of bimetric nature: inside SuSu-cores the spacetime must be flat, whereas the surrounding region, where the matter is compressible and dissipative, the spacetime is Schwarzschild. It is further proposed that the topological change of spacetime is derived by the strong nuclear force, whose operating length scales is found to increase with time to reach O(1) cm at the end of the luminous lifetimes of pulsars. The model presented here model is in line with the recent radio and GW observations of pulsars and NSs.

Detection of magnetic fields in He-rich early B-type stars using HARPSpol

Aims. We focus on early-B type stars with helium overabundance, for which the presence of a magnetic field has not previously been reported. Methods. The measurements were carried out using high-spectral-resolution spectropolarimetric observations obtained with the High Accuracy Radial velocity Planet Searcher (HARPS) in polarimetric mode, installed at the ESO La Silla 3.6 m telescope. Results. For five He-rich stars, the longitudinal magnetic field was detected for the first time. For one target, HD 58260, the presence of a longitudinal magnetic field of the order of 1.8 kG has already been reported in the literature, but the magnetic field has remained constant over tens of years. Our measurement carried out using the polarimetric spectra obtained in 2015 March indicates a slight decrease of the longitudinal magnetic field strength compared to measurements reported in previous works. A search for periodic modulation in available photometric data allowed us to confidently establish a period of 2.64119 ± 0.00420 d in archival ASAS3 data for CPD–27°1791. No period could be determined for the other five stars. Conclusions. The obtained results support the scenario that all He-rich stars are detectably magnetic and form an extension of the Ap star phenomenon to higher temperatures.

Searching for Be Stars in the Open Clusters with PTF/iPTF. I. Cluster Sample and Be Star Candidates

Abstract We conducted a search for Be star candidates in open clusters using Hα imaging photometry of the Palomar Transient Factory Survey to investigate some connections among Be star phenomena, cluster environments, and ages. Stellar members of clusters were identified by spatial distributions, near-infrared magnitudes and colors, and by proper motions. Among 104 open clusters, we identified 96 Be star candidates in 32 clusters; 11 of our candidates have been reported in previous studies. We found that the clusters with age 7.5 &lt; log(t(year)) 8.5 tend to have more Be star candidates; there is about a 40% occurrence rate within this age bin. The clusters in this age bin also tend to have a higher Be fraction N(Be)/N(Be+B-type). These results suggest that the environments of young and intermediate clusters are favorable to the formation of Be phenomena. Spatial distribution of Be star candidates with different ages implies that they do not form preferentially in the central regions. Furthermore, we showed that the mid-infrared (MIR) colors of the Be star candidates are similar to known Be stars, which could be caused by free–free emission or bound-free emission. Some Be star candidates might have no circumstellar dust according to their MIR colors. Finally, among 96 Be candidates, we discovered that one Be star candidate FSR 0904-1 exhibits long-term variability on the timescale of ∼2000 days with an amplitude of 0.2–0.3 mag, indicating a long timescale of disk evolution.

An UXor among FUors: Extinction-related Brightness Variations of the Young Eruptive Star V582 Aur

Abstract V582 Aur is an FU Ori-type young eruptive star in outburst since ∼1985. The eruption is currently in a relatively constant plateau phase, with photometric and spectroscopic variability superimposed. Here we will characterize the progenitor of the outbursting object, explore its environment, and analyze the temporal evolution of the eruption. We are particularly interested in the physical origin of the two deep photometric dips, one that occurred in 2012 and one that is ongoing since 2016. We collected archival photographic plates and carried out new optical, infrared, and millimeter-wave photometric and spectroscopic observations between 2010 and 2018, with a high sampling rate during the current minimum. Besides analyzing the color changes during fading, we compiled multiepoch spectral energy distributions and fitted them with a simple accretion disk model. Based on pre-outburst data and a millimeter continuum measurement, we suggest that the progenitor of the V582 Aur outburst is a low-mass T Tauri star with average properties. The mass of an unresolved circumstellar structure, probably a disk, is 0.04 M ⊙. The optical and near-infrared spectra demonstrate the presence of hydrogen and metallic lines, show the CO band head in absorption, and exhibit a variable Hα profile. The color variations strongly indicate that both the ∼1 yr long brightness dip in 2012 and the current minimum since 2016 are caused by increased extinction along the line of sight. According to our accretion disk models, the reddening changed from A V = 4.5 to 12.5 mag, while the accretion rate remained practically constant. Similarly to the models of the UXor phenomenon of intermediate- and low-mass young stars, orbiting disk structures could be responsible for the eclipses.

The Time-domain Spectroscopic Survey: Target Selection for Repeat Spectroscopy

Abstract As astronomers increasingly exploit the information available in the time domain, spectroscopic variability in particular opens broad new channels of investigation. Here we describe the selection algorithms for all targets intended for repeat spectroscopy in the Time Domain Spectroscopic Survey (TDSS), part of the extended Baryon Oscillation Spectroscopic Survey within the Sloan Digital Sky Survey (SDSS)-IV. Also discussed are the scientific rationale and technical constraints leading to these target selections. The TDSS includes a large “repeat quasar spectroscopy” (RQS) program delivering ∼13,000 repeat spectra of confirmed SDSS quasars, and several smaller “few-epoch spectroscopy” (FES) programs targeting specific classes of quasars as well as stars. The RQS program aims to provide a large and diverse quasar data set for studying variations in quasar spectra on timescales of years, a comparison sample for the FES quasar programs, and an opportunity for discovering rare, serendipitous events. The FES programs cover a wide variety of phenomena in both quasars and stars. Quasar FES programs target broad absorption line quasars, high signal-to-noise ratio normal broad line quasars, quasars with double-peaked or very asymmetric broad emission line profiles, binary supermassive black hole candidates, and the most photometrically variable quasars. Strongly variable stars are also targeted for repeat spectroscopy, encompassing many types of eclipsing binary systems, and classical pulsators like RR Lyrae. Other stellar FES programs allow spectroscopic variability studies of active ultracool dwarf stars, dwarf carbon stars, and white dwarf/M dwarf spectroscopic binaries. We present example TDSS spectra and describe anticipated sample sizes and results.