Short-term variability and mass loss in Be stars V. Space photometry and ground-based spectroscopy of $γ$ Cas
Camilla C. Borre, Dietrich Baade, Andrzej Pigulski, Despina Panoglou, Achim Weiss, Thomas Rivinius, Gerald Handler, Anthony F. J. Moffat, Adam Popowicz, Gregg A… 展开作者
Camilla C. Borre, Dietrich Baade, Andrzej Pigulski, Despina Panoglou, Achim Weiss, Thomas Rivinius, Gerald Handler, Anthony F. J. Moffat, Adam Popowicz, Gregg A. Wade, Werner W. Weiss, Konstanze Zwintz
备注：
13 pages, 12 figures. Accepted for publication in A&A
Context. Be stars are physically complex systems that continue to challenge theory to understand their rapid rotation, complex variability and decretion disks. $γ$ Cassiopeiae ($γ$ Cas) is one such star but is even more curious because of its unexplained hard thermal X-ray emission. Aims. We aim to examine the optical variability of $γ$ Cas and thereby to shed more light on its puzzling behaviour. Methods. Three hundred twenty-one archival H$α$ spectra from 2006 to 2017 are analysed to search for frequencies corresponding to the 203.5 day orbit of the companion. Space photometry from the SMEI satellite from 2003 to 2011 and the BRITE-Constellation of nano-satellites between 2015 and 2019 is investigated in the period range from a couple of hours to a few days. Results. The orbital period of the companion of 203.5 days is confirmed with independent measurements from the structure of the H$α$ line emission. A strong blue/red asymmetry in the amplitude distribution across the H$α$ emission line could hint at a spiral structure in the decretion disk. With the space photometry, the known frequency of 0.82 d$^{-1}$ is confirmed in data from the early 2000s. A higher frequency of 2.48 d$^{-1}$ is present in the data from 2015 to 2019 and possibly also in the early 2000s. A third frequency at 1.25 d$^{-1}$ is proposed to exist in both SMEI and BRITE data. The only explanation covering all three rapid variations seems to be nonradial pulsation. The two higher frequencies are incompatible with rotation.
We present multi-telescope, ground-based, multiwavelength optical and near-infrared photometry of the variable L3.5 ultra-cool dwarf 2MASSW J0036159+182110. We present 22 nights of photometry of 2MASSW J0036159+182110, including 7 nights of simultaneous, multiwavelength photometry, spread over ~120 days allowing us to determine the rotation period of this ultra-cool dwarf to be 3.080 +/- 0.001 hr. Our many nights of multiwavelength photometry allow us to observe the evolution, or more specifically the lack thereof, of the light curve over a great many rotation periods. The lack of discernible …
This work reports a photometric monitoring of the intermediate polar cataclysmic variable star FO Aqr. This is part of the ongoing OAUNI stellar variability program. Around 1200 individual measurements (or $\sim$ 9 hrs of observations) were gathered distributed in five nights. The observation epoch was coincident with the 2016 low state brightness of FO Aqr. Good quality light curves detect unambiguously the expected stellar variability of FO~Aqr. The analysis using periodograms let to determine the main two known periods, P$_{1}$~=~20.380~$\pm$~.003~min and P$_{2}$~=~11.076~$\pm$~.001~min. Ou…
Luminous Blue Variables (LBVs) are massive stars that are likely to be a transitionary phase between O stars and hydrogen-free classical Wolf-Rayet stars. The variability of these stars has been an area of study for both professional and amateur astronomers for more than a century. In this paper, we present five years of precision photometry of the classical LBV P Cygni taken with the BRITE-Constellation nanosatellites. We have analyzed these data with Fourier analysis to search for periodicities that could elucidate the drivers of variability for these stars. These data show some long-timesca…
Stellar evolution models are most uncertain for evolved massive stars. Asteroseismology based on high-precision uninterrupted space photometry has become a new way to test the outcome of stellar evolution theory and was recently applied to a multitude of stars, but not yet to massive evolved supergiants.Our aim is to detect, analyse and interpret the photospheric and wind variability of the O9.5Iab star HD 188209 from Kepler space photometry and long-term high-resolution spectroscopy. We used Kepler scattered-light photometry obtained by the nominal mission during 1460d to deduce the photometr…
We present the results of a J, H, and K photometric variability survey of the central 0.78 square degrees of the young OB association Cygnus OB2. We used data observed with the Wide-Field CAMera at the United Kingdom Infrared Telescope in 2007 (spanning 217 days) to investigate the light curves of 5083 low mass candidate members in the association and explore the occurrence and main characteristics of their near-infrared variability. We identified 2529 stars ($\sim$50$\%$ of the sample) with significant variability with time-scales ranging from days to months. We classified the variable stars …
In early-type Be stars, groups of nonradial pulsation (NRP) modes with numerically related frequencies may be instrumental for the release of excess angular momentum through mass-ejection events. Difference and sum/harmonic frequencies often form additional groups. The goal of this study is to find out whether a similar frequency pattern occurs in the cooler third-magnitude B7-8\,IIIe shell star $ν$ Pup. Time-series analyses are performed of space photometry with BRITE-Constellation (2015, 2016/17, and 2017/18), SMEI (2003--011), and Hipparcos (1989-1993). Two IUE SWP and 27 optical echelle sp…
We present the second results of an ensemble and systematic survey of oscillation mode variability in compact pulsators observed with the original {\sl Kepler} mission. Two types of flux calibrations, raw and corrected, collected on two hot B subdwarf stars, KIC\,2438324 and KIC\,11179657, are thoroughly examined with the goal to evaluate the difference of patterns when oscillation modes modulate in amplitude (AM) and frequency (FM). We concentrate on AMs and FMs occurring in seven multiplet components in each star as representative frequencies. The analysis shows that FM measurements are inde…
Photometry from the Kepler mission is optimized to detect small, short duration signals like planet transits at the expense of long-term trends. This long-term variability can be recovered in photometry from the Full Frame Images (FFIs), a set of calibration data collected approximately monthly during the Kepler mission. Here, we present f3, an open-source package to perform photometry on the Kepler FFIs in order to detect changes in the brightness of stars in the Kepler field of view over long time baselines. We apply this package to a sample of 4,000 Sun-like stars with measured rotation per…
V348 Sgr is simultaneously an active hot R Coronae Borealis (RCB) variable, a peculiar extreme helium star, and the hydrogen-deficient central star of a planetary nebula. Explaining the RCB-type variability has been difficult since the star spends much of its time at minimum light. We present new ground-based multicolour photometry covering 5 observing seasons and 80 days of continuous photometry from space. The latter demonstrate small-amplitude (< 0.01 mag.) variability at maximum light on timescales typical for strange-mode pulsation in hot helium supergiants. These could provide a trigger …
Unsupervised learning for variability detection with Gaia DR3 photometry. The main sequence-white dwarf valley
Radboud University（拉波德大学）；KU Leuven（荷语鲁汶大学）；University of Surrey（萨里大学）；Universitat de Barcelona（巴塞罗那大学）；University of Cape Town（开普敦大学）；South African Astronomical Observatory（南非天文台）；The Inter-University Institute for Data Intensive Astronomy, University of Cape Town（开普敦大学数据密集型天文学跨大学研究所）；Hamburger Sternwarte, University of Hamburg（汉堡天文台，汉堡大学）；Texas Tech University（德克萨斯理工大学）
Large-scale variability in macroturbulence driven by pulsations in the rapidly rotating massive star Zeta Oph from high-cadence ESPRESSO spectroscopy and TESS photometry
Close binary interactions perform a key role in the formation and shaping of planetary nebulae. However only a small fraction of Galactic planetary nebulae are known to host close binary systems. Many such systems are detectable through photometric variability. We searched recently published epoch photometry data from Gaia DR3 for planetary nebula central stars with periodic photometric variability indicative of binarity, uncovering four previously unknown close binaries.
We present an analysis of oscillation mode variability in the hot B subdwarf star EPIC~220422705, a new pulsator discovered from $\sim78$~days of {\em K}2 photometry. The high-quality light curves provide a detection of 66 significant independent frequencies, from which we identified 9 incomplete potential triplets and 3 quintuplets. Those {\sl g-} and {\sl p-}multiplets give rotation periods of $\sim$ 36 and 29 days in the core and at the surface, respectively, potentially suggesting a slightly differential rotation. We derived a period spacing of 268.5\,s and 159.4\,s for the sequence of dip…
Empirical evidence for the involvement of nonradial pulsations (NRP's) in the mass loss from Be stars ranges from (i) a singular case (\object{$μ$ Cen}) of repetitive mass ejections triggered by multi-mode beating to (ii) several photometric reports about enormous numbers of pulsation modes popping up during outbursts and on to (iii) effective single-mode pulsators. The BRITE Constellation of nanosatellites was used to obtain mmag photometry of the Be stars $η$ and \object{$μ$ Cen}. In the low-inclination star \object{$μ$ Cen}, light pollution by variable amounts of near-stellar matter prevent…
Results from optical CCD photometric observations of 13 pre-main-sequence stars collected during the period from February 2007 to November 2020 are presented. These stars are located in the association Cepheus OB3, in the field of the young star V733 Cephei. Photometric observations, especially concerning the long-term variability of the stars, are missing in the literature. We present the first long-term $V(RI)_{c}$ monitoring for them, that cover 13 years. Results from our study indicate that all of the investigated stars manifest strong photometric variability. The presented paper is a part…
The symphony of pulsations and binarity among massive stars using HERMES spectroscopy and TESS photometry
Newcastle University（纽卡斯尔大学）；KU Leuven（荷语鲁汶大学）；University of Amsterdam（阿姆斯特丹大学）；Tel Aviv University（特拉维夫大学）；Royal Observatory of Belgium（比利时皇家天文台）；Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences（波兰科学院尼古拉·哥白尼天文学中心）
The BRITE Constellation of nanosatellites obtained mmag photometry of 28 Cygni for 11 months in 2014-2016. Observations with the Solar Mass Ejection Imager in 2003-2010 and 118 H$α$ line profiles were added. For decades, 28 Cyg has exhibited four large-amplitude frequencies: two closely spaced frequencies of spectroscopically confirmed $g$ modes near 1.5 c/d, one slightly lower exophotospheric (Stefl) frequency, and at 0.05 c/d the difference frequency between the two g modes. This top-level framework is indistinguishable from eta Cen (Paper I), which is also very similar in spectral type, rot…
Context. Massive stars are predicted to excite internal gravity waves (IGWs) by turbulent core convection and from turbulent pressure fluctuations in their near-surface layers. These IGWs are extremely efficient at transporting angular momentum and chemical species within stellar interiors, but they remain largely unconstrained observationally. Aims. We aim to characterise the photometric detection of IGWs across a large number of O and early-B stars in the Hertzsprung-Russell diagram, and explain the ubiquitous detection of stochastic variability in the photospheres of massive stars. Methods.…
Context. Modern space telescopes are currently providing high-precision light curves for a large fraction of the sky, such that many new variable stars are being discovered. However, some stars have periodic variability with periods of order minutes and require high-cadence photometry to probe the physical mechanisms responsible. A cadence of less than a minute is often required to remove Nyquist ambiguities and confirm rapid variability which forces observers to obtain high-cadence ground-based photometry. Aims. We aim to provide a modern software package to reduce ground-based photometric ti…
We present the time series analysis of seven B-type stars (HD 121790, HD 122980, HD 129116, HD 133242, HD 144294, HD 145482, and HD 145502) observed with the BRITE satellites. Furthermore, we located these stars in the Hertzsprung-Russell-diagram. One rotational induced variable (HD 122980, P~80 d) and one binary (HD 145502, P~5.6 d) showing variability due to ellipsoidal variation and/or reflection were detected.
The tidal interaction of a Be star with a binary companion forms two spiral arms that cause orbital modulation of the Be disc structure. The aim of this work is to identify observables in which this modulation is apparent. The structure of a Be disc in a coplanar circular binary system is computed with a smoothed-particle hydrodynamics code, and a radiation transfer code calculates the spectral energy distribution. Line depolarisation was confirmed, with polarisation profiles nearly reverse to emission-line profiles. The continuum flux maximizes for pole-on discs, but photometric variability m…
Determination of stellar age is a crucial task in astrophysics research. Different methods are nowadays used either model dependent or based on calibrated empirical relations. The most reliable results are generally obtained when different methods are used in complementary way. We propose a new method for the age determination of young stellar associations and open clusters (ages < 125 Myr), which can allow to further constrain the age when used together with other methods. We explore the amplitude of the photometric variability in bins of color and rotation period of five young associations a…
The physics of magnetic hot stars and how a large-scale magnetic field affects their interior properties is largely unknown. Few studies have combined high-quality observations and modelling of magnetic pulsating stars, known as magneto-asteroseismology, primarily because of the dearth of detected pulsations in stars with a confirmed and well-characterised large-scale magnetic field. We aim to characterise observational signatures of rotation and pulsation in chemically peculiar candidate magnetic stars using photometry from the K2 space mission. Thus, we identify the best candidate targets fo…
We present 17 nights of ground-based, near-infrared photometry of the variable L/T transition brown dwarf SIMP J013656.5+093347 and an additional 3 nights of ground-based photometry of the radio-active late M-dwarf TVLM 513-46546. Our TVLM 513-46546 photometry includes 2 nights of simultaneous, multiwavelength, ground-based photometry, in which we detect obvious J-band variability, but do not detect I-band variability of similar amplitude, confirming that the variability of TVLM 513-46546 most likely arises from clouds or aurorae, rather than starspots. Our photometry of SIMP J013656.5+093347 …
The variability induced by precipitable water vapour (PWV) can heavily affect the accuracy of time-series photometric measurements gathered from the ground, especially in the near-infrared. We present here a novel method of modelling and mitigating this variability, as well as open-sourcing the developed tool -- Umbrella. In this study, we evaluate the extent to which the photometry in three common bandpasses (r', i', z'), and SPECULOOS' primary bandpass (I+z'), are photometrically affected by PWV variability. In this selection of bandpasses, the I+z' bandpass was found to be most sensitive to…
We present an 80-d long uninterrupted high-cadence K2 light curve of the B1Iab supergiant rho Leo (HD 91316), deduced with the method of halo photometry. This light curve reveals a dominant frequency of $f_{\rmrot}=0.0373$d$^{-1}$ and its harmonics. This dominant frequency corresponds with a rotation period of 26.8d and is subject to amplitude and phase modulation. The K2 photometry additionally reveals multiperiodic low-frequency variability ($<1.5 $d$^{-1}$) and is in full agreement with low-cadence high-resolution spectroscopy assembled during 1800 days. The spectroscopy reveals rotational …
We present the first four years of BVRI photometry from an on-going survey to annually monitor the photometric behavior of evolved luminous stars in M31 and M33. Photometry was measured for 199 stars at multiple epochs, including 9 classic Luminous Blue Variables (LBVs), 22 LBV candidates, 10 post-RGB A/F type hypergiants, and 18 B[e] supergiants. At all epochs the brightness is measured in V and at least one other band to a precision of 0.04 -- 0.10 magnitudes down to a limiting magnitude of 19.0 -- 19.5. Thirty three (33) stars in our survey exhibit significant variability, including at leas…
The most powerful tests of stellar models come from the brightest stars in the sky, for which complementary techniques, such as astrometry, asteroseismology, spectroscopy, and interferometry can be combined. The K2 Mission is providing a unique opportunity to obtain high-precision photometric time series for bright stars along the ecliptic. However, bright targets require a large number of pixels to capture the entirety of the stellar flux, and bandwidth restrictions limit the number and brightness of stars that can be observed. To overcome this, we have developed a new photometric technique, …
High-precision K2/TESS Photometry and HERMES Spectroscopy of Four Bright Field Stars
Mbarara University of Science and Technology（姆巴拉拉科技大学）；Kyambogo University（坎博戈大学）；Max-Planck-Institut für Sonnensystemforschung（马克斯·普朗克太阳系研究所）；Aryabhatta Research Institute of Observational Sciences（阿亚班达观测科学研究所）；Max-Planck-Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Institute of Astronomy, KU Leuven（鲁汶大学天文研究所）；Royal Observatory of Belgium（比利时皇家天文台）
Space observatories have provided unprecedented depictions of the many variability behaviors typical of low-mass, young stars. However, those studies have so far largely omitted more massive objects ($\sim$2 $M_\odot$ to 4-5 $M_\odot$), and were limited by the absence of simultaneous, multi-wavelength information. We present a new study of young star variability in the $\sim$1-2 Myr-old, massive Lagoon Nebula region. Our sample encompasses 278 young, late-B to K-type stars, monitored with Kepler/K2. Auxiliary $u,g,r,i,Hα$ time series photometry, simultaneous with K2, was acquired at the Parana…
Classical Be stars are introduced as object class and their particular potential for space based photometry is highlighted. A brief summary of the various types of variability observed in Be stars makes clear that an interpretation of every single frequency as a pulsation mode falls short, instead there are as well purely circumstellar variations and those that originate in the immediate stellar to circumstellar interaction region. In particular the latter offer great potential, as they are linked to one of the few remaining great riddles of Be stars, namely how they feed their disks.
The rapidly oscillating Ap (roAp) stars exhibit pulsational photometric and/or radial velocity variations on time scales of several minutes, which are essential to test current pulsation models as well as our assumptions of atmospheric structure characteristics. In addition, their chemical peculiarity makes them very interesting for probing stellar formation and evolution in the presence of a global magnetic field. To date, a limited number of only 61 roAp stars are known to show photometric variability. On the other hand, a literature survey yields 619 unique stars that have unsuccessfully be…
Refined reduction and standardisation of 53 years of UBV photometry at Hvar
University of Zagreb, Faculty of Geodesy（萨格勒布大学地理学院）；Charles University, Faculty of Mathematics and Physics（查理大学数学物理学院）；Université de Liège, GAPHE, STAR（列日大学GAPHE STAR）；Astronomical Institute of the Czech Academy of Sciences（捷克科学院天文研究所）
