H. Korhonen
A5075547985- Stellar, planetary, and galactic studies
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Solar and Space Plasma Dynamics
- Adaptive optics and wavefront sensing
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Geophysics and Gravity Measurements
- Galaxies: Formation, Evolution, Phenomena
- Particle Accelerators and Free-Electron Lasers
- Astrophysics and Cosmic Phenomena
- Particle accelerators and beam dynamics
- History and Developments in Astronomy
- High-pressure geophysics and materials
- Isotope Analysis in Ecology
- Calibration and Measurement Techniques
- Radio Astronomy Observations and Technology
- Atmospheric Ozone and Climate
- Magnetic confinement fusion research
- SAS software applications and methods
- Geomagnetism and Paleomagnetism Studies
- Planetary Science and Exploration
University of Copenhagen
2013-2024
European Southern Observatory
2020-2024
Max Planck Institute for Astronomy
2024
Keele University
2019
Turku Centre for Computer Science
2011-2017
University of Turku
2011-2017
The Open University
2016
Sharif University of Technology
2016
Natural History Museum Aarhus
2011-2015
European Southern Observatory
2008-2015
Over the duration of Kepler mission, KIC8462852 was observed to undergo irregularly shaped, aperiodic dips in flux up $\sim 20$\%. The dipping activity can last for between 5 and 80 days. We characterize object with high-resolution spectroscopy, spectral energy distribution fitting, radial velocity measurements, imaging, Fourier analyses light curve. determine that is a typical main-sequence F3 V star exhibits no significant IR excess, has very close interacting companions. In this paper, we...
Abstract Study Analysis Group 21 (SAG21) of NASA’s Exoplanet Exploration Program was organized to study the effect stellar contamination on space-based transmission spectroscopy, a method for studying exoplanetary atmospheres by measuring wavelength-dependent radius planet as it transits its star. Transmission spectroscopy relies precise understanding spectrum star being occulted. However, stars are not homogeneous, constant light sources but have temporally evolving photospheres and...
Tight relationships exist in the local universe between central stellar properties of galaxies and mass their supermassive black hole. These suggest holes co-evolve, with main regulation mechanism being energetic feedback from accretion onto hole during its quasar phase. A crucial question is how relationship evolves time; a key epoch to probe this at peaks star formation growth 8-12 billion years ago (redshifts 1-3). Here we report dynamical measurement luminous redshift 2, look back time...
We study the time variations of cycles 20 active stars based on decades-long photometric or spectroscopic observations. A method time-frequency analysis, as discussed in a companion paper, is applied to data. Fifteen definitely show multiple cycles; records rest are too short verify timescale for second cycle. The typically systematic changes. For three stars, we found two each them that not harmonics, and which vary parallel, indicating common physical mechanism arising from dynamo...
We present preliminary asteroseismic results from Kepler on three G-type stars. The observations, made at one-minute cadence during the first 33.5d of science operations, reveal high signal-to-noise solar-like oscillation spectra in all stars: About 20 modes may be clearly distinguished each star. discuss appearance spectra, use frequencies and frequency separations to provide radii, masses ages stars, comment light these prospects for inference other solar-type stars that will observe.
We report the detection of a Cold Neptune m_planet=21+/-2MEarth orbiting 0.38MSol M dwarf lying 2.5-3.3 kpc toward Galactic center as part campaign combining ground-based and Spitzer observations to measure distribution planets. This is first time that complex real-time protocols described by Yee et al. (2015), which aim maximize planet sensitivity while maintaining sample integrity, have been carried out in practice. Multiple survey follow-up teams successfully combined their efforts within...
The ultrafast-rotating (Prot ≈ 0.44 d) fully convective single M4 dwarf V374 Peg is a well-known laboratory for studying intense stellar activity in stable magnetic topology. As an observable proxy the field, we study stability of light curve, hence spot configuration. We also measure occurrence rate flares and coronal mass ejections (CMEs). have analysed spectroscopic observations, BV(RI)C photometry covering 5 yrs, additional RC that expands temporal base over 16 yr. curve suggests almost...
Flares and CMEs can have deleterious effects on their surroundings: they erode atmospheres of orbiting planets over time also high importance in stellar evolution. Most the CME detections literature are single events found serendipitously sparse for statistical investigation. We aimed to gather a large amount spectral data M-dwarfs drastically increase number known make analysis possible order study properties potential CMEs. Using archive we investigated asymmetric features Balmer-lines,...
Time domain science has undergone a revolution over the past decade, with tens of thousands new supernovae (SNe) discovered each year. However, several observational domains, including SNe within days or hours explosion and faint, red transients, are just beginning to be explored. Here, we present Young Supernova Experiment (YSE), novel optical time-domain survey on Pan-STARRS telescopes. Our is designed obtain well-sampled $griz$ light curves for transient events up $z \approx 0.2$. This...
The CRyogenic InfraRed Echelle Spectrograph (CRIRES) Upgrade project CRIRES$^{+}$ extended the capabilities of CRIRES. It transformed this VLT instrument into a cross-dispersed spectrograph to increase wavelength range that is covered simultaneously by up factor ten. In addition, new detector focal plane array three Hawaii 2RG detectors with 5.3 $\mu$m cutoff replaced existing detectors. Amongst many other improvements, spectropolarimetric unit was added and calibration system has been...
Ultra-hot Jupiters are tidally locked with their host stars, dividing atmospheres into a hot dayside and colder nightside. As the planet moves through transit, different regions of atmosphere rotate view, revealing chemical regimes. Highresolution spectrographs can observe asymmetries velocity shifts offer possibility for time-resolved spectroscopy. The ultra-hot Jupiter WASP-189 b has recently been found to possess rich transmission spectrum evidence atmospheric dynamics inhomogeneity. In...
Aims. The present study was conducted to determine the optical extinction curve for Cerro Paranal under typical clear-sky observing conditions, with purpose of providing community a function be used correct observed spectra, an accuracy 0.01 mag airmass-1. Additionally, this work meant analyze variability various components, derive main atmospheric parameters, and set term reference future studies, especially in view construction Extremely Large Telescope on nearby Armazones.
We present time-series photometric observations of thirteen transits in the planetary systems WASP-24, WASP-25 and WASP-26. All three have orbital obliquity measurements, WASP-24 WASP-26 been observed with Spitzer, was previously comparatively neglected. Our light curves were obtained using telescope-defocussing method scatters 0.5 to 1.2 mmag relative their best-fitting geometric models. used these data measure physical properties ephemerides high precision, finding that our improved...
We report 13 high-precision light curves of eight transits the exoplanet WASP-52b, obtained by using four medium-class telescopes, through different filters, and adopting defocussing technique. One transit was recorded simultaneously from two observatories another one same site but with instruments, including a multi-band camera. Anomalies were clearly detected in five modelled as starspots occulted planet during events. fitted clean jktebop code, those anomalies prism+gemc codes order to...
The ubiquity of M dwarf stars combined with their low masses and luminosities make them prime targets in the search for nearby, habitable exoplanets. We investigate effects starspot-induced radial velocity (RV) jitter on detection characterization planets orbiting dwarfs. create surface spot configurations both random coverage active regions. Synthetic stellar spectra are calculated from a given map, RV measurements obtained using cross-correlation technique. add signal an planet to these...
At low redshift, a handful of gamma-ray bursts (GRBs) have been discovered with peak luminosities ($L_{\rm iso} < 10^{48.5}~\rm{erg\,s}^{-1}$) substantially lower than the average more distant ones > 10^{49.5}~\rm{erg\,s}^{-1}$). The properties several low-luminosity (low-$L$) GRBs indicate that they can be due to shock break-out, as opposed emission from ultrarelativistic jets. Owing this, it is highly debated how both populations are connected, and whether there continuum between them....
We present microlens parallax measurements for 21 (apparently) isolated lenses observed toward the Galactic bulge that were imaged simultaneously from Earth and Spitzer, which was ∼1 AU west of in projection. combine these with a kinematic model Galaxy to derive distance estimates each lens, error bars are small compared Sun's galactocentric distance. The ensemble therefore yields well-defined cumulative distribution lens distances. In principle, it is possible compare this against set...
WASP-80 is one of only two systems known to contain a hot Jupiter which transits its M-dwarf host star. We present eight light curves transit event, obtained simultaneously using defocussed telescopes. These data were taken through the Bessell I, Sloan griz and near-infrared JHK passbands. use our search for opacity-induced changes in planetary radius, but find that all values agree with each other. Our are therefore consistent flat transmission spectrum within observational uncertainties....
We present 17 transit light curves of the ultrashort period planetary system WASP-103, a strong candidate for detection tidally-induced orbital decay. use these to establish high-precision reference epoch timing studies. The time mid-point is now measured an accuracy 4.8 s, versus 67.4 s in discovery paper, aiding future searches With help published spectroscopic measurements and theoretical stellar models, we determine physical properties high precision detailed error budget calculations....
Abstract We have carried out a detailed investigation of eclipsing binary star NT Aps using high cadence photometric observations from the TESS satellite and time-series spectra EFOSC2 at ESO’s New Technology Telescope. have, for first time, determined precise system parameters this W UMa-type late-type contact binary. Our analysis indicates that is composed two solar-like stars with mass ratio $q=0.31$ orbital period 0.29475540 $\pm$ 0.00000035 days. These values are typical common envelope...
We present a search for stellar activity (flares and mass ejections) in sample of 28 stars the young open cluster Blanco-1. use optical spectra obtained with European Southern Observatory's Visible Multi-Object Spectrograph installed on Very Large Telescope. From total observing time ∼5 h, we find four Hα flares but no distinct indication coronal ejections (CMEs) investigated dK–dM stars. Two show 'dips' their light curves right before impulsive phases which are similar to previous...