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Aims .Over the past decades, libraries of stellar spectra have been used in a large variety of science cases, including as sources of reference spectra for a given object or a given spectral type. Despite the existence of large libraries and the increasing number of projects of large-scale spectral surveys, there is to date only one very high-resolution spectral library offering spectra from a few hundred objects from the southern hemisphere (UVES-POP). We aim to extend the sample, offering a finer coverage of effective temperatures and surface gravity with a uniform collection of spectra obtained in the northern hemisphere. Methods .Between 2010 and 2020, we acquired several thousand echelle spectra of bright stars with the Mercator-HERMES spectrograph located in the Roque de Los Muchachos Observatory in La Palma, whose pipeline offers high-quality data reduction products. We have also developed methods to correct for the instrumental response in order to approach the true shape of the spectral continuum. Additionally, we have devised a normalisation process to provide a homogeneous normalisation of the full spectral range for most of the objects. Results .We present a new spectral library consisting of 3256 spectra covering 2043 stars. It combines high signal-to-noise and high spectral resolution over the entire range of effective temperatures and luminosity classes. The spectra are presented in four versions: raw, corrected from the instrumental response, with and without correction from the atmospheric molecular absorption, and normalised (including the telluric correction)., SCOPUS: ar.j, info:eu-repo/semantics/published

We report on the discovery of a planetary companion candidate with a minimum mass M sin i = 4.6 ± 1.0 MJupiter orbiting the K2 III giant star HD 175370 (KIC 007940959). This star was a target in our programme to search for planets around a sample of 95 giant stars observed with Kepler. This detection was made possible using precise stellar radial velocity measurements of HD 175370 taken over five years and four months using the coudé echelle spectrograph of the 2-m Alfred Jensch Telescope and the fibre-fed echelle spectrograph High Efficiency and Resolution Mercator Echelle Spectrograph of the 1.2-m Mercator Telescope. Our radial velocity measurements reveal a periodic (349.5 ± 4.5 d) variation with a semi-amplitude K = 133 ± 25ms-1, superimposed on a long-term trend. A low-mass stellar companion with an orbital period of ~88 yr in a highly eccentric orbit and a planet in a Keplerian orbit with an eccentricity e = 0.22 are the most plausible explanation of the radial velocity variations. However, we cannot exclude the existence of stellar envelope pulsations as a cause for the low-amplitude radial velocity variations and only future continued monitoring of this system may answer this uncertainty. From Kepler photometry, we find that HD 175370 is most likely a low-mass red giant branch or asymptotic giant branch star., SCOPUS: ar.j, info:eu-repo/semantics/published

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provide evidence of monoperiodic variations with a frequency of 0.7572 d-1 and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g. Mn and Y). In contrast, lines of other elements do not show significant variations. As found in otherHgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star. © 2013 ESO., SCOPUS: ar.j, info:eu-repo/semantics/published

The existence of pulsations in HgMn stars is still being debated. To provide the first unambiguous observational detection of pulsations in this class of chemically peculiar objects, the bright star HD 45975 was monitored for nearly two months by the CoRoT satellite. Independent analyses of the light curve provide evidence of monoperiodic variations with a frequency of 0.7572 d-1 and a peak-to-peak amplitude of ~2800 ppm. Multisite, ground-based spectroscopic observations overlapping the CoRoT observations show the star to be a long-period, single-lined binary. Furthermore, with the notable exception of mercury, they reveal the same periodicity as in photometry in the line moments of chemical species exhibiting strong overabundances (e.g. Mn and Y). In contrast, lines of other elements do not show significant variations. As found in otherHgMn stars, the pattern of variability consists in an absorption bump moving redwards across the line profiles. We argue that the photometric and spectroscopic changes are more consistent with an interpretation in terms of rotational modulation of spots at the stellar surface. In this framework, the existence of pulsations producing photometric variations above the ~50 ppm level is unlikely in HD 45975. This provides strong constraints on the excitation/damping of pulsation modes in this HgMn star. © 2013 ESO., SCOPUS: ar.j, info:eu-repo/semantics/published

We present a light-curve analysis and radial velocity study of KOI-74, an eclipsing A star + white dwarf binary with a 5.2-d orbit. Aside from new spectroscopy covering the orbit of the system, we used 212d of publicly available Kepler observations and present the first complete light-curve fitting to these data, modelling the eclipses and transits, ellipsoidal modulation, reflection and Doppler beaming. Markov chain Monte Carlo simulations are used to determine the system parameters and uncertainty estimates. Our results are in agreement with earlier studies, except that we find an inclination of 87°0 ± 0°.4, which is significantly lower than the previously published value. The altered inclination leads to different values for the relative radii of the two stars and therefore also the mass ratio deduced from the ellipsoidal modulations seen in this system. We find that the mass ratio derived from the radial velocity amplitude (q= 0.104 ± 0.004) disagrees with that derived from the ellipsoidal modulation (q= 0.052 ± 0.004 assuming corotation). This was found before, but with our smaller inclination, the discrepancy is even larger than previously reported. Accounting for the rapid rotation of the A-star, instead of assuming corotation with the binary orbit, is found to increase the discrepancy even further by lowering the mass ratio to q= 0.047 ± 0.004. These results indicate that one has to be extremely careful in using the amplitude of an ellipsoidal modulation signal in a close binary to determine the mass ratio, when a proof of corotation is not firmly established. The same problem could arise whenever an ellipsoidal modulation amplitude is used to derive the mass of a planet orbiting a host star that is not in corotation with the planet's orbit. The radial velocities that can be inferred from the detected Doppler beaming in the light curve are found to be in agreement with our spectroscopic radial velocity determination. We also report the first measurement of R, SCOPUS: ar.j, info:eu-repo/semantics/published

We present a light-curve analysis and radial velocity study of KOI-74, an eclipsing A star + white dwarf binary with a 5.2-d orbit. Aside from new spectroscopy covering the orbit of the system, we used 212d of publicly available Kepler observations and present the first complete light-curve fitting to these data, modelling the eclipses and transits, ellipsoidal modulation, reflection and Doppler beaming. Markov chain Monte Carlo simulations are used to determine the system parameters and uncertainty estimates. Our results are in agreement with earlier studies, except that we find an inclination of 87°0 ± 0°.4, which is significantly lower than the previously published value. The altered inclination leads to different values for the relative radii of the two stars and therefore also the mass ratio deduced from the ellipsoidal modulations seen in this system. We find that the mass ratio derived from the radial velocity amplitude (q= 0.104 ± 0.004) disagrees with that derived from the ellipsoidal modulation (q= 0.052 ± 0.004 assuming corotation). This was found before, but with our smaller inclination, the discrepancy is even larger than previously reported. Accounting for the rapid rotation of the A-star, instead of assuming corotation with the binary orbit, is found to increase the discrepancy even further by lowering the mass ratio to q= 0.047 ± 0.004. These results indicate that one has to be extremely careful in using the amplitude of an ellipsoidal modulation signal in a close binary to determine the mass ratio, when a proof of corotation is not firmly established. The same problem could arise whenever an ellipsoidal modulation amplitude is used to derive the mass of a planet orbiting a host star that is not in corotation with the planet's orbit. The radial velocities that can be inferred from the detected Doppler beaming in the light curve are found to be in agreement with our spectroscopic radial velocity determination. We also report the first measurement of R, SCOPUS: ar.j, info:eu-repo/semantics/published