Context. Exoplanet searches have revealed interesting correlations between the stellar properties and the occurrence rate of planets. In particular, different independent surveys have demonstrated that giant planets are preferentially found around metal-rich stars and that their fraction increases with the stellar mass. Aims. During the past six years we have conducted a radial velocity follow-up program of 166 giant stars to detect substellar companions and to characterize their orbital properties. Using this information, we aim to study the role of the stellar evolution in the orbital parameters of the companions and to unveil possible correlations between the stellar properties and the occurrence rate of giant planets. Methods. We took multi-epoch spectra using FEROS and CHIRON for all of our targets, from which we computed precision radial velocities and derived atmospheric and physical parameters. Additionally, velocities computed from UCLES spectra are presented here. By studying the periodic radial velocity signals, we detected the presence of several substellar companions. Results. We present four new planetary systems around the giant stars HIP 8541, HIP 74890, HIP 84056, and HIP 95124. Additionally, we study the correlation between the occurrence rate of giant planets with the stellar mass and metallicity of our targets. We find that giant planets are more frequent around metal-rich stars, reaching a peak in the detection of f = 16.7 +15.5 −5.9 % around stars with [Fe/H] ∼ 0.35 dex. Similarly, we observe a positive correlation of the planet occurrence rate with the stellar mass, between M ∼ 1.0 and 2.1 M , with a maximum of f = 13.0Conclusions. We conclude that giant planets are preferentially formed around metal-rich stars. In addition, we conclude that they are more efficiently formed around more massive stars, in the stellar mass range of ∼1.0-2.1 M . These observational results confirm previous findings for solar-type and post-MS hosting stars, and provide further support to the core-accretion formation model.

We report the discovery of a substellar companion around the giant star HIP 67537. Based on precision radial velocity measurements from CHIRON and FEROS high-resolution spectroscopic data, we derived the following orbital elements for HIP 67537 b: m b sini= 11.1 +0.4 −1.1 M jup , a = 4.9 +0.14 −0.13 AU and e = 0.59 +0.05 −0.02 . Considering random inclination angles, this object has 65% probability to be above the theoretical deuterium-burning limit, thus it is one of the few known objects in the planet to brown-dwarf transition region. In addition, we analyzed the Hipparcos astrometric data of this star, from which we derived a minimum inclination angle for the companion of ∼ 2 deg. This value corresponds to an upper mass limit of ∼ 0.3 M ⊙ , therefore the probability that HIP 67537 b is stellar in nature is 7%. The large mass of the host star and the high orbital eccentricity makes HIP 67537 b a very interesting and rare substellar object. This is the second candidate companion in the brown dwarf desert detected in the sample of intermediate-mass stars targeted by the EXPRESS radial velocity program, which corresponds to a detection fraction of f = 1.6 +2.0 −0.5 %. This value is larger than the fraction observed in solar-type stars, providing new observational evidence of an enhanced formation efficiency of massive substellar companions in massive disks. Finally, we speculate about different formation channels for this object.

We report the discovery of TOI-677 b, first identified as a candidate in light curves obtained within Sectors 9 and 10 of the Transiting Exoplanet Survey Satellite (TESS ) mission and confirmed with radial velocities. TOI-677 b has a mass of M p = 1.236 +0.069 −0.067 M J , a radius of R P = 1.170 ± 0.03 R J , and orbits its bright host star (V = 9.8 mag) with an orbital period of 11.23660 ± 0.00011 d, on an eccentric orbit with e = 0.435 ± 0.024. The host star has a mass of M = 1.181 ± 0.058 M , a radius of R = 1.28 +0.03 −0.03 R , an age of 2.92 +0.80 −0.73 Gyr and solar metallicity, properties consistent with a main sequence late F star with T eff = 6295 ± 77 K. We find evidence in the radial velocity measurements of a secondary long term signal which could be due to an outer companion. The TOI-677 b system is a well suited target for Rossiter-Mclaughlin observations that can constrain migration mechanisms of close-in giant planets.

SN 2011ja was a bright (I = -18.3) Type II supernova occurring in the nearby edge on spiral galaxy NGC 4945. Flat-topped and multi-peaked Hα and Hβ spectral emission lines appear between 64 -84 days post-explosion, indicating interaction with a disc-like circumstellar medium inclined 30-45 degrees from edge-on. After day 84 an increase in the H-and K-band flux along with heavy attenuation of the red wing of the emission lines are strong indications of early dust formation, likely located in the cool dense shell created between the forward shock of the SN ejecta and the reverse shock created as the ejecta plows into the existing CSM. Radiative transfer modeling reveals both ≈ 1.5 × 10 −4 M ⊙ of pre-existing dust located ∼ 10 16.7 cm away and ≈ 5 × 10 −5 M ⊙ of newly formed dust. Spectral observations after 1.5 years reveal the possibility that the fading SN is located within a young (3-6 Myr) massive stellar cluster, which when combined with tentative 56 Ni mass estimates of 0.2 M ⊙ may indicate a massive (≥ 25 M ⊙ ) progenitor for SN 2011ja.

Using robotic telescopes of the Universitätssternwarte Bochum near Cerro Armazones in Chile, we monitored the z = 0.0377 Seyfert-1 galaxy WPVS48 (2MASX J09594263-3112581) in the optical (B and R) and near-infrared (NIR, J and K s ) with a cadence of two days. The light curves show unprecedented variability details. The NIR variation features of WPVS48 are consistent with the corresponding optical variations, but the features appear sharper in the NIR than in the optical, suggesting that the optical photons undergo multiple scatterings. The J and K s emission, tracing the hot (∼1600 K) dust echo, lags the B and R variations by on average τ = 64 ± 4 days and 71 ± 5 days, respectively (restframe). WPVS48 lies on the known τ − M V relationship. However, the observed lag τ is about three times shorter than expected from the dust sublimation radius r sub inferred from the optical-UV luminosity, and explanations for this common discrepancy are searched for. The sharp NIR echos argue for a face-on torus geometry and allow us to put forward two potential scenarios: 1) as previously proposed, in the equatorial plane of the accretion disk the inner region of the torus is flattened and may come closer to the accretion disk. 2) The dust torus with inner radius r sub is geometrically and optically thick, so that the observer only sees the facing rim of the torus wall, which lies closer to the observer than the torus equatorial plane and therefore leads to an observed foreshortened lag. Both scenarios are able to explain the factor three discrepancy between τ and r sub . Longer-wavelength dust reverberation data might enable one to distinguish between the scenarios.