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New multicolour photometric observations were carried out on 22 nights in three observation missions between 2015 October and 2016 February for eclipsing binary HIP 7666. High- and low-resolution spectroscopic observations were also carried out in the winters of 2015, 2016, and 2019, respectively. The fully phase-covered light curves and radial velocity curves are presented. All times of light minima are used to calculate the orbital period [2.372 2200(4) d] and new ephemerides. The photometric solution and stellar physical parameters are derived, showing that HIP 7666 is a detached binary with the absolute parameters M1 = 1.53(3) M⊙, R1 = 2.08(2) R⊙, log L1/L⊙ = 0.99(3), log g1 = 3.98(2), Mbol1 = 2.26(8), Teff,1 = 7100(100) K for the primary, and M2 = 1.23(3) M⊙, R2 = 1.06(2) R⊙, log L2/L⊙ = 0.13(4), log g2 = 4.47(2), Mbol2 = 4.4(1), Teff,2 = 6029(67) K for the secondary. The age of 1.69 Gyr and 1.755 Gyr are estimated from parsec isochrones and mesa evolutionary tracks, respectively. In Herzsprung–Russell (H–R) diagram, the primary component has evolved to the late stages, while the secondary still locates at the early stages of the main sequence. Frequency analysis yields three frequencies of f1 = 24.631(4) cd−1, f2 = 21.193(1) cd−1, and f3 = 28.07(7) cd−1. Comparisons between models and observations suggest that the primary component is most likely a p-mode non-radial δ Scuti oscillator.

Context. The rotation period of stars is an important parameter together with mass, radius, and effective temperature. It is an essential parameter for any radial velocity monitoring, as stellar activity can mimic the presence of a planet at the stellar rotation period. Several methods exist to measure it, including long sequences of photometric measurements or temporal series of stellar activity indicators. Aims. Here, we use the circular polarization in near-infrared spectral lines for a sample of 43 quiet M dwarfs and compare the measured rotation periods to those obtained with other methods. Methods. From Stokes V spectropolarimetric sequences observed with SPIRou at the Canada-France-Hawaii Telescope and the data processed with the APERO pipeline, we computed the least-squares deconvolution profiles using different masks of atomic stellar lines with known Landé factor appropriate to the effective temperature of the star. We derived the longitudinal magnetic field to examine its possible variation in 50 to 200 observations of each star. To determine the stellar rotation period, we applied a Gaussian process regression, enabling us to determine the rotation period of stars with evolving longitudinal field. Results. We were able to measure a rotation period for 27 of the 43 stars of our sample. The rotation period was previously unknown for 8 of these stars. Our rotation periods agree well with periods found in the literature based on photometry and activity indicators, and we confirm that near-infrared spectropolarimetry is an important tool for measuring rotation periods, even for magnetically quiet stars. Furthermore, we computed the ages for 20 stars of our sample using gyrochronology.

Aims: We investigate magnetic tracers in the photosphere and the chromosphere of the ultra-rapid rotator ($P\sim0.32d$) V530 Per, a cool member of the open cluster $\alpha$ Persei, to characterize the short-term variability of the magnetic activity and large-scale magnetic field of this prototypical young, rapidly rotating solar-like star. Methods: With time-resolved spectropolarimetric observations spread over four close-by nights, we reconstructed the brightness distribution and large-scale magnetic field geometry of V530 Per through Zeeman-Doppler imaging. Simultaneously, we estimated the short-term variability of the surface through latitudinal differential rotation. Using the same data set, we also mapped the spatial distribution of prominences through tomography of H$\alpha$ emission. Results: As in our previous study, a large dark spot occupies the polar region of V530 Per with smaller, dark, and bright spots at lower latitudes. The large-scale magnetic field is dominated by a toroidal, mostly axisymmetric component. The maximal radial field strength is equal to $\sim1$ kG. The surface differential rotation is consistent with a smooth Sun-like shear d$\Omega = 0.053 \pm 0.004$ rad.d$^{-1}$, close to the solar shear level. The prominence pattern displays a stable component that is confined close to the corotation radius. We also observe rapidly evolving H$\alpha$ emitting structures, over timescales ranging from minutes to days. The fast H$\alpha$ evolution was not linked to any detected photospheric changes in the spot or magnetic coverage., Comment: Accepted by A&A, 17 pages, 13 figures

Phase \RNum{2} of the LAMOST-{\sl Kepler/K}2 survey (LK-MRS), initiated in 2018, aims at collecting medium-resolution spectra ($R\sim7,500$; hereafter MRS) for more than $50,000$ stars with multiple visits ($\sim60$ epochs) over a period of 5 years (2018 September to 2023 June). We selected 20 footprints distributed across the {\sl Kepler} field and six {\sl K}2 campaigns, with each plate containing a number of stars ranging from $\sim2,000$ to $\sim 3,000$. During the first year of observations, the LK-MRS has already collected $\sim280,000$ and $\sim369,000$ high-quality spectra in the blue and red wavelength range, respectively. The atmospheric parameters and radial velocities for $\sim259,000$ spectra of $21,053$ targets were successfully calculated by the LASP pipeline. The internal uncertainties for the effective temperature, surface gravity, metallicity, and radial velocity are found to be $100$\,K, $0.15$\,dex, $0.09$\,dex, and $1.00$\,km\,s$^{-1}$, respectively. We found $14,997$, $20,091$, and $1,514$ stars in common with the targets from the LAMOST low-resolution survey (LRS), GAIA and APOGEE, respectively, corresponding to a fraction of $\sim70\%$, $\sim95\%$ and $\sim7.2\%$. In general, the parameters derived from LK-MRS spectra are consistent with those obtained from the LRS and APOGEE spectra, but the scatter increases as the surface gravity decreases when comparing with the measurements from APOGEE. A large discrepancy is found with the GAIA values of the effective temperature. The comparisons of radial velocities of LK-MRS to GAIA and LK-MRS to APOGEE nearly follow an Gaussian distribution with a mean $\mu\sim1.10$ and $0.73$\,km\,s$^{-1}$, respectively., Comment: 24 pages, 15 figures, 4 tables, ApJS, accepted

An increasing number of white dwarf stars show atmospheric chemical composition polluted by heavy elements accreted from debris disk material. The existence of such debris disks strongly suggests the presence of one or more planet(s) whose gravitational interaction with rocky planetesimals is responsible for their disruption by tidal effect. The ZZ Ceti pulsator and polluted DAZ white dwarf GD 133 is a good candidate for searching for such a potential planet. We started in 2011 a photometric follow-up of its pulsations. As a result of this work in progress, we used the data gathered from 2011 to 2015 to make an asteroseismological analysis of GD 133, providing the star parameters from a best fit model with $M$/$M_{\odot}$ = 0.630 $\pm$ 0.002, $T_{\rm eff}$ = 12400 K $\pm$ 70 K, log($M_{\rm He}/M$) = -2.00 $\pm$ 0.02, log($M_{\rm H}/M$) = -4.50 $\pm$ 0.02 and determining a rotation period of $\approx$ 7 days., 10 pages, 13 figures, accepted by MNRAS

Time-series, multi-color photometry and high-resolution spectra of the short period eclipsing binary V Tri were obtained by observations. The completely covered light and radial velocity curves of the binary system are presented. All times of light minima derived from both photoelectric and CCD photometry were used to calculate the orbital period and new ephemerides of the eclipsing system. The analysis of $O-C$ diagram reveals that the orbital period is $0.58520481\ days$, decreasing at a rate of $dP/dt=-7.80\times10^{-8} d\ yr^{-1} $. The mass transfer between the two components and the light time-travel effect due to a third body could be used to explain the period decrease. However, a semidetached configuration with the less-mass component filling and the primary nearly filling each of their Roche lobes was derived from the synthesis of the light and radial velocity curves by using the 2015 version of the Wilson-Devinney code. We consider the period decrease to be the nonconservative mass transfer from the secondary component to the primary and the mass loss of the system, which was thought to be an EB type while it should be an EA type (semi-detached Algol-type) from our study. The masses, radii and luminosities of the primary and secondary are $1.60\pm0.07 M_\odot$, $1.64\pm0.02 R_\odot$, $14.14\pm0.73 L_\odot$ and $0.74\pm0.02 M_\odot$, $1.23\pm0.02 R_\odot$, $1.65\pm0.05 L_\odot$, respectively., Comment: 11 pages, 6 figures, Accepted for publication by AJ

This paper presents a photometric and spectroscopic study of the short-period binary star Cl*~Melotte~111~AV~1224. Measurements in the $B$, $V$, and $R$ passbands obtained during three observing runs between 2014 and 2017 and medium-resolution spectra secured in 2014, are analyzed together with public data from the SuperWASP and LAMOST projects. Our light curves show marked asymmetry with a variable O'Connell effect. The SuperWASP photometry is used to derive a mean binary period of 0.345225 days. The analysis of the $(O-C)$ diagram reveals that the orbital period is decreasing at a rate of $dP/dt = -3.87 \times 10^{-6}$ days yr$^{-1}$, which may be caused by mass transfer from the more-massive component to the less-massive one. The system is found to be a single-lined spectroscopic binary with a systemic velocity, $\gamma = 1 \pm 3$ Km s$^{-1}$, and a semi-amplitude, K$_{1}$ = 21 $\pm$ 5 Km s$^{-1}$. The spectral classification and the effective temperature of the primary component are estimated to be K0V $\pm$ 1 and $5200 \pm 150$ K, respectively. The photometric and spectroscopic solutions reveal that Cl*~Melotte~111~AV~1224 is a low-mass ratio ($q=m_{2}/m_{1} \sim 0.11$), low-inclination ($\sim ~ 38^{\circ}$) near-contact system. The masses, radii and luminosity for the primary and secondary are estimated to be $1.02 \pm 0.06\, M_\odot$, $1.23 \pm 0.05\, R_\odot $, $1.01 \pm 0.06\, L_\odot$ and $0.11 \pm 0.08\, M_\odot$, $0.45 \pm 0.05\, R_\odot$, $0.10 \pm 0.06\, L_\odot$, respectively. The marginal contact, together with the period decrease, suggests that this binary system may be at a key evolutionary stage, as predicted by the theory of thermal relaxation oscillations., Comment: Accepted for publication in PASP; 11 pages, 11 figures, 8 tables

Based on spectroscopic observations for the eclipsing binaries CSTAR 036162 and CSTAR 055495 with the WiFeS/2.3 m telescope at SSO and CSTAR 057775 with the Mage/Magellan I at LCO in 2017, stellar parameters are derived. More than 100 nights of almost-continuous light curves reduced from the time-series photometric observations by CSTAR at Dome A of Antarctic in i in 2008 and in g and r in 2009, respectively, are applied to find photometric solutions for the three binaries with the Wilson-Devinney code. The results show that CSTAR 036162 is a detached configuration with the mass ratio q = 0.354 +/- 0.0009, while CSTAR 055495 is a semi-detached binary system with the unusual q = 0.946 +/- 0.0006, which indicates that CSTAR 055495 may be a rare binary system with mass ratio close to one and the secondary component filling its Roche Lobe. This implies that a mass-ratio reversal has just occurred and CSTAR 055495 is in a rapid mass-transfer stage. Finally, CSTAR 057775 is believed to be an A-type W UMa binary with q = 0.301 +/- 0.0008 and a fill-out factor of f = 0.742(8).

We investigate signatures of magnetic fields and activity at the surface and in the prominence system of the ultra-rapid rotator V530 Per, a G-type solar-like member of the young open cluster $\alpha$~Persei. This object has a rotation period shorter than all stars with available magnetic maps. With a time-series of spectropolarimetric observations gathered with ESPaDOnS over 2 nights on the CFHT, we reconstruct the surface brightness and large-scale magnetic field of V530 Per using the Zeeman-Doppler imaging method, assuming an oblate stellar surface. We also estimate the short term evolution of the brightness distribution through latitudinal differential rotation. Using the same data set, we finally map the spatial distribution of prominences through tomography of the H\alpha emission. The brightness map is dominated by a large, dark spot near the pole, accompanied by a complex distribution of bright and dark features at lower latitudes. The magnetic field map is reconstructed as well, most of the large-scale magnetic field energy is stored in the toroidal field component. The main radial field structure is a positive region of about 500 G, at the location of the dark polar spot. The brightness map of V530 Per is sheared by solar-like differential rotation, with a roughly solar value for the difference in rotation rate between the pole and equator. \halpha~is observed in emission, and is mostly modulated by the stellar rotation period. The prominence system is organized in a ring at the approximate location of the co-rotation radius, with significant evolution between the two observing nights. V530 Per is the first example of a solar-type star to have its surface magnetic field and prominences mapped together, which will bring important observational constraints to better understand the role of slingshot prominences in the angular momentum evolution of the most active stars., Comment: Accepted by A&A, 20 pages, 14 figures