arXiv subjects

E. Kambe

Publications and source records attributed to E. Kambe.

At least 19 recordsLinked to original sources

arXiv2024

Gliese 12 b: A temperate Earth-sized planet at 12 pc ideal for atmospheric transmission spectroscopy

Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period ($P_{\rm{orb}}$) of 12.76 days. The planet, Gliese 12b, was initially identified as a candidate with an ambiguous $P_{\rm{orb}}$ from TESS data. We confirmed the transit signal and $P_{\rm{orb}}$ using ground-based photometry with MuSCAT2 and MuSCAT3, and validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host star is inactive, with an X-ray-to-bolometric luminosity ratio of $\log L_{\rm X}/L_{\rm bol} \approx -5.7$. Joint analysis of the light curves and RV measurements revealed that Gliese 12b has a radius of 0.96 $\pm$ 0.05 $R_\oplus$, a 3$\sigma$ mass upper limit of 3.9 $M_\oplus$, and an equilibrium temperature of 315 $\pm$ 6 K assuming zero albedo. The transmission spectroscopy metric (TSM) value of Gliese 12b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12b to the small list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.

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arXiv2023

Detached Eclipsing Binaries in Compact Hierarchical Triples: Triple-lined systems BD+44 2258 and KIC 06525196

Compact Hierarchical Triples (CHT) are systems with the tertiary star orbiting the inner binary in an orbit shorter than 1000 days. CHT with an eclipsing binary as its inner binary can help us extract a multitude of information about all three stars in the system. In this study, we use independent observational techniques to estimate the orbital, stellar, and atmospheric parameters of two triple-lined CHT: BD+442258 and KIC06525196. We find that the masses of stars in BD+442258 are $1.011\pm0.029 M_{\odot}$, $0.941\pm0.033 M_{\odot}$, and $0.907\pm0.065 M_{\odot}$ while in KIC06525196 the estimated masses are $1.0351\pm0.0055 M_{\odot}$, $0.9712\pm0.0039 M_{\odot}$, and $0.777\pm0.012 M_{\odot}$. Using spectral disentangling, we obtained individual spectra of all the stars and combined them with light curve modeling to obtain radii, metallicities, and temperatures. Using stellar evolution models from MESA, we constrain the log(age) of BD+442258 to be 9.89 and 9.49 for KIC06525196. Two stars in BD+442258 are found to be sub-giants while all three stars in KIC06525196 are main-sequence stars. We constrain the mutual inclinations to certain angles for BD+442258 and KIC06525196 using numerical integration. Integrating with tidal interaction schemes and stellar evolution models, we find that KIC06525196 is a stable system. But the inner binary of BD+442258 merges within 550 Myrs. The time of this merger is affected by the orientation of the tertiary, even rushing the collapse by 100 Myrs when the mutual inclination is close to 90 degrees.

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arXiv2023

Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya

The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 $\pm$ 20 Myr and found that both binary components are situated in the Delta Scuti instability strip. The frequency analysis revealed pulsation frequencies between the 5.5 - 13.0 d$^{-1}$ and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.

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arXiv2022

The near-core rotation of HD 112429: a gamma Doradus star with TESS photometry and legacy spectroscopy

The TESS space mission provides us with high-precision photometric observations of bright stars over more than 70% of the entire sky, allowing us to revisit and characterise well-known stars. We aim to conduct an asteroseismic analysis of the gamma Doradus star HD112429 using both the available ground-based spectroscopy and TESS photometry, and assess the conditions required to measure the near-core rotation rate and buoyancy travel time. We collect and reduce the available five sectors of short-cadence TESS photometry of this star, as well as 672 legacy observations from six medium- to high-resolution ground-based spectrographs. We determine the stellar pulsation frequencies from both data sets using iterative prewhitening, do asymptotic g mode modelling of the star and investigate the corresponding spectral line profile variations using the pixel-by-pixel method. We validate the pulsation frequencies from the TESS data up to $S/N \geq 5.6$, confirming recent reports in the literature that the classical criterion $S/N \geq 4$ does not suffice for space-based observations. We identify the pulsations as prograde dipole g modes and r-mode pulsations, and measure a near-core rotation rate of $1.536(3) d^{-1}$ and a buoyancy travel time $Π_0$ of 4190(50) s. These results are in agreement with the observed spectral line profile variations, which were qualitatively evaluated using a newly developed toy model. We establish a set of conditions that have to be fulfilled for an asymptotic asteroseismic analysis of g-mode pulsators. In the case of HD112429, two TESS sectors of space photometry suffice. Although a detailed asteroseismic modelling analysis is not viable for g-mode pulsators with only short or sparse light curves of space photometry, we find that it is possible to determine global asteroseismic quantities for a subset of these stars. (abbreviated.)

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arXiv2021

Orbital and physical parameters of eclipsing binaries from the ASAS catalogue -- XII. A sample of systems with $K2$ photometry

We present results of the analysis of light and radial velocity (RV) curves of eight detached eclipsing binaries observed by the All-Sky Automated Survey, which we have followed up with high-resolution spectroscopy, and were later observed by the $Kepler$ satellite as part of the $K2$ mission. The RV measurements came from spectra obtained with OAO-188/HIDES, MPG-2.2m/FEROS, SMARTS 1.5m/CHIRON, Euler/CORALIE, ESO-3.6m/HARPS, and OHP-1.93/ELODIE instruments. The $K2$ time-series photometry was analyzed with the JKTEBOP code, with out-of-eclipse modulations of different origin taken into account. Individual component spectra were retrieved with the FD3 code, and analyzed with the code iSpec in order to determine effective temperatures and metallicities. Absolute values of masses, radii, and other stellar parameters are calculated, as well as ages, found through isochrone fitting. For five systems such analysis has been done for the first time. The presented sample consists of a variety of stars, from low-mass dwarfs, through G and F-type Main Sequence objects, to evolved active sub-giants, one of which is found to be crossing the Hertzsprung gap. One target may contain a $γ$ Dor-type pulsator, two more are parts of higher-order multiples, and spectra of their tertiaries were also retrieved and used to constrain the properties of these systems.

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arXiv2019

HIDES spectroscopy of bright detached eclipsing binaries from the $Kepler$ field - III. Spectral analysis, updated parameters, and new systems

We present the latest results of our spectroscopic observations and refined modelling of a sample of detached eclipsing binaries (DEBs), selected from the $Kepler$} Eclipsing Binary Catalog, that are also double-lined spectroscopic binaries (SB2). New high resolution spectra obtained with the HIDES spectrograph, attached to the 1.88-m telescope of the Okayama Astrophysical Observatory supplemented the previous observations, allowing to improve physical parameters of some systems, and characterize three previously omitted. All the obtained radial velocities (RVs) were combined with $Kepler$ photometry, in order to derive a full set of orbital and physical parameters. Ten out of eleven SB2s have their component spectra tomographically disentangled, and spectral analysis was performed with iSpec, in order to derive effective temperatures of components and metallicities of the systems. By comparing our results with theoretical models, we assess the age and evolutionary status of the studied objects. We find a good match to all but one systems. We have derived distances from thus determined parameters, and compare them with those from the $Gaia$ Data Release 2. For systems previously studied by other authors, our new results lead to better consistency between observations and models.

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arXiv2017

A Jupiter-mass planet around the K0 giant HD 208897

For over 10 years, we have carried out a precise radial velocity (RV) survey to find substellar companions around evolved G,K-type stars to extend our knowledge of planet formation and evolution. We performed high precision RV measurements for the giant star HD 208897 using an iodine (I2) absorption cell. The measurements were made at TÜBİTAK National Observatory (TUG, RTT150) and Okayama Astrophysical Observatory (OAO). For the origin of the periodic variation seen in the RV data of the star, we adopted a Keplerian motion caused by an unseen companion. We found that the star hosts a planet with a minimum mass of m2sini=1.40MJ, which is relatively low compared to those of known planets orbiting evolved intermediate-mass stars. The planet is in a nearly circular orbit with a period of P=353 days at about 1 AU distance from the host star. The star is metal rich and located at the early phase of ascent along the red giant branch. The photometric observations of the star at Ankara University Kreiken Observatory (AUKR) and the HIPPARCOS photometry show no sign of variation with periods associated with the RV variation. Neither bisector velocity analysis nor analysis of the Ca II and Halpha lines shows any correlation with the RV measurements.

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arXiv2017

High-resolution spectroscopy and abundance analysis of Delta Scuti stars near the Gamma Doradus instability strip

$δ$ Scuti stars are remarkable objects for asteroseismology. In spite of decades of investigations, there are still important questions about these pulsating stars to be answered, such as their positions in $\log$$T_{\rm eff}$ $-$ $\log g$ diagram, or the dependence of the pulsation modes on atmospheric parameters and rotation. Therefore, we performed a detailed spectroscopic study of $41$ $δ$ Scuti stars. The selected objects are located near the $γ$ Doradus instability strip to make a reliable comparison between both types of variables. Spectral classification, stellar atmospheric parameters ($T_{\rm eff}$, $\log g$, $ξ$) and $v \sin i$ values were determined. The spectral types and luminosity classes of stars were found to be A1$-$F5 and III$-$V, respectively. The $T_{\rm eff}$ ranges from $6600$ to $9400$ K, whereas the obtained $\log g$ values are from $3.4$ to $4.3$. The $v \sin i$ values were found between $10$ and $222$ km s$^{-1}$. The derived chemical abundances of $δ$ Scuti stars were compared to those of the non-pulsating stars and $γ$ Doradus variables. It turned out that both $δ$ Scuti and $γ$ Doradus variables have similar abundance patterns, which are slightly different from the non-pulsating stars. These chemical differences can help us to understand why there are non-pulsating stars in classical instability strip. Effects of the obtained parameters on pulsation period and amplitude were examined. It appears that the pulsation period decreases with increasing $T_{\rm eff}$. No significant correlations were found between pulsation period, amplitude and $v \sin i$.

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arXiv2017

KIC 4150611: a rare multi-eclipsing quintuple with a hybrid pulsator

We present the results of our analysis of KIC 4150611 (HD 181469) - an interesting, bright quintuple system that includes a hybrid $δ$ Sct/$γ$ Dor pulsator. Four periods of eclipses - 94.2, 8.65, 1.52 and 1.43 d - have been observed by the Kepler satellite, and three point sources (A, B, and C) are seen in high angular resolution images. From spectroscopic observations made with the HIDES spectrograph attached to the 1.88-m telescope of the Okayama Astrophysical Observatory (OAO), for the first time we calculated radial velocities (RVs) of the component B - a pair of G-type stars - and combined them with Kepler photometry in order to obtain absolute physical parameters of this pair. We also managed to directly measure RVs of the pulsator, also for the first time. Additionally, we modelled the light curves of the 1.52 and 1.43-day pairs, and measured their eclipse timing variations (ETVs). We also performed relative astrometry and photometry of three sources seen on the images taken with the NIRC2 camera of the Keck II telescope. Finally, we compared our results with theoretical isochrones. The brightest component Aa is the hybrid pulsator, transited every 94.2 days by a pair of K/M-type stars (Ab1+Ab2), which themselves form a 1.52-day eclipsing binary. The components Ba and Bb are late G-type stars, forming another eclipsing pair with a 8.65 day period. Their masses and radii are $M_{Ba}=0.894\pm0.010$ M$_\odot$, $R_{Ba}=0.802\pm0.044$ R$_\odot$ for the primary, and $M_{Bb}=0.888\pm0.010$ M$_\odot$, $R_{Bb}=0.856\pm0.038$ R$_\odot$ for the secondary. The remaining period of 1.43 days is possibly related to a faint third star C, which itself is most likely a background object. The system's properties are well-represented by a 35 Myr isochrone. There are also hints of additional bodies in the system.

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arXiv2017

HIDES spectroscopy of bright detached eclipsing binaries from the $Kepler$ field - I. Single-lined objects

We present results of our spectroscopic observations of nine detached eclipsing binaries (DEBs), selected from the $Kepler$ Eclipsing Binary Catalog, that only show one set of spectral lines. Radial velocities (RVs) were calculated from the high resolution spectra obtained with the HIDES instrument, attached to the 1.88-m telescope at the Okayama Astrophysical Observatory, and from the public APOGEE archive. In our sample we found five single-lined binaries, with one component dominating the spectrum. The orbital and light curve solutions were found for four of them, and compared with isochrones, in order to estimate absolute physical parameters and evolutionary status of the components. For the fifth case we only update the orbital parameters, and estimate the properties of the unseen star. Two other systems show orbital motion with a period known from the eclipse timing variations (ETVs). For these we obtained parameters of outer orbits, by translating the ETVs to RVs of the centre of mass of the eclipsing binary, and combining with the RVs of the outer star. Of the two remaining ones, one is most likely a blend of a faint background DEB with a bright foreground star, which lines we see in the spectra, and the last case is possibly a quadruple bearing a sub-stellar mass object. Where possible, we compare our results with literature, especially with results from asteroseismology. We also report possible detections of solar-like oscillations in our RVs.

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arXiv2017

HIDES spectroscopy of bright detached eclipsing binaries from the $Kepler$ field - II. Double- and triple-lined objects

We present the results of our spectroscopic observations of eight detached eclipsing binaries (DEBs), selected from the $Kepler$ Eclipsing Binary Catalog. Radial velocities (RVs) were calculated from high resolution spectra obtained with the HIDES pectrograph, attached to the 1.88-m telescope of the Okayama Astrophysical Observatory, and were used to characterize the targets in combination with the $Kepler$ light curves. For each binary we obtained a full set of orbital and physical parameters, reaching precision below 3% in masses and radii for 5 pairs. By comparing our results with theoretical models, we assess the distance, age and evolutionary status of the researched objects. We also study eclipse timing variations of selected objects, and identify a new system with a $γ$Dor pulsator. Two systems are triples, and show lines coming from three components. In one case the motion of the outer star and the perturbation in the RVs of the inner binary are clearly visible and periodical, which allows us to directly calculate the mass of the third star, and inclination of the outer orbit. In the second case we only see a clear motion of the tertiary, and investigate two scenarios: that it is a linear trend coming from the orbital motion around the inner binary, and that it is caused by a planetary mass companion. When possible, we also compare our results with the literature, and conclude that only by combining photometry with RVs it is possible to obtain correct physical parameters of both components of a DEB.

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arXiv2015

Multiples among detached eclipsing binaries from the ASAS catalog

For more than three years now we have been conducting a spectroscopic survey of detached eclipsing binaries (DEBs) from the All-Sky Automated Survey (ASAS) database. Thousands of high-resolution spectra of over 300 systems were secured, and used for radial velocity measurements and spectral analysis. In our sample we found a zoo of multiple systems, such as spectroscopic triples and quadruples, visual binaries with eclipsing components, and circumbinary low-mass companions, including sub-stellar-mass candidates

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arXiv2014

Detection of solar-like oscillations in the bright red giant stars $γ$ Psc and $θ^1$ Tau from a 190-day high-precision spectroscopic multisite campaign

Red giants are evolved stars which exhibit solar-like oscillations. Although a multitude of stars have been observed with space telescopes, only a handful of red-giant stars were targets of spectroscopic asteroseismic observing projects. We search for solar-like oscillations in the two bright red-giant stars $γ$ Psc and $θ^1$ Tau from time series of ground-based spectroscopy and determine the frequency of the excess of oscillation power $ν_{max}$ and the mean large frequency separation $Δν$ for both stars. The radial velocities of $γ$ Psc and $θ^1$ Tau were monitored for 120 and 190 days, respectively. Nearly 9000 spectra were obtained. To reach the accurate radial velocities, we used simultaneous thorium-argon and iodine-cell calibration of our optical spectra. In addition to the spectroscopy, we acquired VLTI observations of $γ$ Psc for an independent estimate of the radius. Also 22 days of observations of $θ^1$ Tau with the MOST-satellite were analysed. The frequency analysis of the radial velocity data of $γ$ Psc revealed an excess of oscillation power around 32 $μ$Hz and a large frequency separation of 4.1$\pm$0.1$μ$Hz. $θ^1$ Tau exhibits oscillation power around 90 $μ$Hz, with a large frequency separation of 6.9$\pm$0.2$μ$Hz. Scaling relations indicate that $γ$ Psc is a star of about $\sim$1 M$_\odot$ and $\sim$10 R$_\odot$. $θ^1$ Tau appears to be a massive star of about $\sim$2.7 M$_\odot$ and $\sim$11 R$_\odot$. The radial velocities of both stars were found to be modulated on time scales much longer than the oscillation periods. While the mass of $θ^1$ Tau is in agreement with results from dynamical parallaxes, we find a lower mass for $γ$ Psc than what is given in the literature. The long periodic variability agrees with the expected time scales of rotational modulation.

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arXiv2013

Extensive study of HD 25558, a long-period double-lined binary with two SPB components

We carried out an extensive observational study of the Slowly Pulsating B (SPB) star, HD 25558. The ~2000 spectra obtained at different observatories, the ground-based and MOST satellite light curves revealed that this object is a double-lined spectroscopic binary with an orbital period of about 9 years. The observations do not allow the inference of an orbital solution. We determined the physical parameters of the components, and found that both lie within the SPB instability strip. Accordingly, both show line-profile variations due to stellar pulsations. Eleven independent frequencies were identified in the data. All the frequencies were attributed to one of the two components based on Pixel-by-pixel variability analysis of the line profiles. Spectroscopic and photometric mode identification was also performed for the frequencies of both stars. These results suggest that the inclination and rotation of the two components are rather different. The primary is a slow rotator with ~6 d period, seen at ~60 deg inclination, while the secondary rotates fast with ~1.2 d period, and is seen at ~20 inclination. Spectropolarimetric measurements revealed that the secondary component has a magnetic field with at least a few hundred Gauss strength, while no magnetic field can be detected in the primary.

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arXiv2012

Multisite spectroscopic seismic study of the beta Cep star V2052 Oph: inhibition of mixing by its magnetic field

We used extensive ground-based multisite and archival spectroscopy to derive observational constraints for a seismic modelling of the magnetic beta Cep star V2052 Ophiuchi. The line-profile variability is dominated by a radial mode (f_1=7.14846 d^{-1}) and by rotational modulation (P_rot=3.638833 d). Two non-radial low-amplitude modes (f_2=7.75603 d^{-1} and f_3=6.82308 d^{-1}) are also detected. The four periodicities that we found are the same as the ones discovered from a companion multisite photometric campaign (Handler et al. 2012) and known in the literature. Using the photometric constraints on the degrees l of the pulsation modes, we show that both f_2 and f_3 are prograde modes with (l,m)=(4,2) or (4,3). These results allowed us to deduce ranges for the mass (M \in [8.2,9.6] M_o) and central hydrogen abundance (X_c \in [0.25,0.32]) of V2052 Oph, to identify the radial orders n_1=1, n_2=-3 and n_3=-2, and to derive an equatorial rotation velocity v_eq \in [71,75] km s^{-1}. The model parameters are in full agreement with the effective temperature and surface gravity deduced from spectroscopy. Only models with no or mild core overshooting (alpha_ov \in [0,0.15] local pressure scale heights) can account for the observed properties. Such a low overshooting is opposite to our previous modelling results for the non-magnetic beta Cep star theta Oph having very similar parameters, except for a slower surface rotation rate. We discuss whether this result can be explained by the presence of a magnetic field in V2052 Oph that inhibits mixing in its interior.

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arXiv2010

A multi-site campaign to measure solar-like oscillations in Procyon. II. Mode frequencies

We have analyzed data from a multi-site campaign to observe oscillations in the F5 star Procyon. The data consist of high-precision velocities that we obtained over more than three weeks with eleven telescopes. A new method for adjusting the data weights allows us to suppress the sidelobes in the power spectrum. Stacking the power spectrum in a so-called echelle diagram reveals two clear ridges that we identify with even and odd values of the angular degree (l=0 and 2, and l=1 and 3, respectively). We interpret a strong, narrow peak at 446 muHz that lies close to the l=1 ridge as a mode with mixed character. We show that the frequencies of the ridge centroids and their separations are useful diagnostics for asteroseismology. In particular, variations in the large separation appear to indicate a glitch in the sound-speed profile at an acoustic depth of about 1000 s. We list frequencies for 55 modes extracted from the data spanning 20 radial orders, a range comparable to the best solar data, which will provide valuable constraints for theoretical models. A preliminary comparison with published models shows that the offset between observed and calculated frequencies for the radial modes is very different for Procyon than for the Sun and other cool stars. We find the mean lifetime of the modes in Procyon to be 1.29 +0.55/-0.49 days, which is significantly shorter than the 2-4 days seen in the Sun.

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arXiv2010

High-dispersion spectroscopic monitoring of the Be/X-ray binary A0535+26/V725 Tau I: The long-term profile variability

We report on optical high-dispersion spectroscopic monitoring observations of the Be/X-ray binary A0535+26/V725 Tau, carried out from November 2005 to March 2009. The main aim of these monitoring observations is to study spectral variabilities in the Be disc, on both the short (a week or so) and long (more than hundreds of days) timescales, by taking long-term frequent observations. Our four-year spectroscopic observations indicate that the V/R ratio, i.e., the relative intensity of the violet (V) peak to the red (R) one, of the double-peaked H-alpha line profile varies with a period of 500 days. The H-beta line profile also varies in phase with the H-alpha profile. With these observations covering two full cycles of the V/R variability, we reconstruct the 2-D structure of the Be disc by applying the Doppler tomography method to the H-alpha and H-beta emission line profiles, using a rigidly rotating frame with the V/R variability period. The resulting disc structure reveals non-axisymmetric features, which can be explained by a one-armed perturbation in the Be disc. It is the first time that an eccentric disc structure is directly detected by using a method other than the interferometric one.

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arXiv2009

An asteroseismic study of the beta Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling

We present the results of a spectroscopic multisite campaign for the beta Cephei star 12 (DD) Lacertae. Our study is based on more than thousand high-resolution high S/N spectra gathered with 8 different telescopes in a time span of 11 months. In addition we make use of numerous archival spectroscopic measurements. We confirm 10 independent frequencies recently discovered from photometry, as well as harmonics and combination frequencies. In particular, the SPB-like g-mode with frequency 0.3428 1/d reported before is detected in our spectroscopy. We identify the four main modes as (l1,m1) = (1, 1), (l2,m2) = (0, 0), (l3,m3) = (1, 0) and (l4,m4) = (2, 1) for f1 = 5.178964 1/d, f2 = 5.334224 1/d, f3 = 5.066316 1/d and f4 = 5.490133 1/d, respectively. Our seismic modelling shows that f2 is likely the radial first overtone and that the core overshooting parameter alpha_ov is lower than 0.4 local pressure scale heights.

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