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Planets orbiting members of open or globular clusters offer a great opportunity to study exoplanet populations systematically, as stars within clusters provide a mostly homogeneous sample, at least in chemical composition and stellar age. However, even though there have been coordinated efforts to search for exoplanets in stellar clusters, only a small number of planets have been detected. One successful example is the seven-year radial velocity (RV) survey `Search for giant planets in M67' of 88 stars in the open cluster M67, which led to the discovery of five giant planets, including three close-in ($P < 10$ days) hot-Jupiters. In this work, we continue and extend the observation of stars in M67, with the aim being to search for additional planets. We conducted spectroscopic observations with the Habitable Planet Finder (HPF), HARPS, HARPS-North, and SOPHIE spectrographs of 11 stars in M67. Six of our targets showed a variation or long-term trends in their RV during the original survey, while the other five were not observed in the original sample, bringing the total number of stars to 93. An analysis of the RVs reveals one additional planet around the turn-off point star S1429 and provides solutions for the orbits of stellar companions around S2207 and YBP2018. S1429 b is a warm-Jupiter on a likely circular orbit with a period of $77.48_ $ days and a minimum mass of $ M i = 1.80 0.2$ M$_ J $. We update the hot-Jupiter occurrence rate in M67 to include the five new stars, deriving $4.2_ <!PCT!>$ when considering all stars, and $5.4_ <!PCT!>$ if binary star systems are removed.
Planets orbiting members of open or globular clusters offer a great opportunity to study exoplanet populations systematically, as stars within clusters provide a mostly homogeneous sample, at least in chemical composition and stellar age. However, even though there have been coordinated efforts to search for exoplanets in stellar clusters, only a small number of planets have been detected. One successful example is the seven-year radial velocity (RV) survey `Search for giant planets in M67' of 88 stars in the open cluster M67, which led to the discovery of five giant planets, including three close-in ($P < 10$ days) hot-Jupiters. In this work, we continue and extend the observation of stars in M67, with the aim being to search for additional planets. We conducted spectroscopic observations with the Habitable Planet Finder (HPF), HARPS, HARPS-North, and SOPHIE spectrographs of 11 stars in M67. Six of our targets showed a variation or long-term trends in their RV during the original survey, while the other five were not observed in the original sample, bringing the total number of stars to 93. An analysis of the RVs reveals one additional planet around the turn-off point star S1429 and provides solutions for the orbits of stellar companions around S2207 and YBP2018. S1429 b is a warm-Jupiter on a likely circular orbit with a period of $77.48_ $ days and a minimum mass of $ M i = 1.80 0.2$ M$_ J $. We update the hot-Jupiter occurrence rate in M67 to include the five new stars, deriving $4.2_ <!PCT!>$ when considering all stars, and $5.4_ <!PCT!>$ if binary star systems are removed.
The fact that the rotation periods of Ap stars span five to six orders of magnitude and that the longest ones reach several hundred years represents one of the main unsolved challenges of stellar physics. Our goal is to gain better understanding of the occurrence and properties of the longest period Ap stars. We obtained high resolution spectra of a sample of super-slowly rotating Ap (ssrAp) star candidates identified by a TESS photometric survey to confirm that they are indeed Ap stars, to check that their projected equatorial velocities are compatible with super-slow rotation, and to obtain a first estimate of their magnetic field strengths. For the confirmed Ap stars, we determined whenever possible their mean magnetic field modulus, their mean quadratic magnetic field, and an upper limit of their projected equatorial velocities. Eighteen of the 27 stars studied are typical Ap stars; most of the other nine appear to be misclassified. One of the Ap stars is not a slow rotator; it must be seen nearly pole-on. The properties of the remaining 17 are compatible with moderately to extremely long rotation periods. Eight new stars with resolved magnetically split lines in the visible range were discovered; their mean magnetic field modulus and their mean quadratic magnetic field were measured. The mean quadratic field could also be determined in five more stars. Five spectroscopic binaries containing an Ap star, which were not previously known, were identified. Among the misclassified stars, one double-lined spectroscopic binary with two similar, sharp-lined Am components was also discovered. The technique that we used to carry out a search for ssrAp star candidates using TESS data is validated. Its main limitation appears to arise from uncertainties in the spectral classification of Ap stars. The new magnetic field measurements obtained as part of this study lend further support to the tentative conclusions of our previous studies: the absence of periods $ in stars with $B_0 the lower rate of occurrence of super-slow rotation for field strengths $B_0 than in the range kG B_0 and the deficiency of slowly rotating Ap stars with (phase-averaged) field strengths between sim 2 and sim 3\,kG.
The magnetic chemically peculiar Ap stars exhibit an extreme spread of rotational velocities, the cause of which is not clearly understood. Ap stars with rotation periods of 50 days or longer are know as super-slowly rotating Ap (ssrAp) stars. Photometrically variable Ap stars are commonly termed $ $ Canum Venaticorum (ACV) variables. Our study aims to enlarge the sample of known ssrAp stars using data from the Zwicky Transient Facility (ZTF) survey to enable more robust and significant statistical studies of these objects. Using selection criteria based on the known characteristics of ACV variables, candidate stars were gleaned from the ZTF catalogues of periodic and suspected variable stars and from ZTF raw data. ssrAp stars were identified from this list via their characteristic photometric properties, Delta a photometry, and spectral classification. The final sample consists of 70 new ssrAp stars, which mostly exhibit rotation periods of between 50 and 200 days. The object with the longest period has a rotation period of 2551.7 days. We present astrophysical parameters and a Hertzsprung-Russell diagram for the complete sample of known ssrAp stars. With very few exceptions, the ssrAp stars are grouped in the middle of the main sequence with ages in excess of 150 Myr. ZTF J021309.72+582827.7 was identified as a possible binary star harbouring an Ap star and a cool component, possibly shrouded in dust. With our study, we enlarge the sample of known ssrAp stars by about 150<!PCT!>, paving the way for more in-depth statistical studies.
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