Leonardos Gkouvelis

Ludwig-Maximilians-University of Munich | LMU · University Observatory

Cooling of Jupiter's auroral thermosphere by H3⁺ radiation to space is one of the processes controlling the energy balance in the auroral upper atmosphere. The UltraViolet Spectrograph (UVS) and the Jupiter InfraRed Auroral Mapper (JIRAM) on board Juno have observed the Jovian polar aurora from its polar orbit since August 2016. The UVS instrument...

The Ultraviolet and Visible Spectrometer Ultraviolet (UVIS UV) and Visible Spectrometer channel of the Nadir and Occultation for MArs Discovery spectrometer aboard the ExoMars Trace Gas Orbiter has made limb observations of the Martian dayglow during more than a Martian year. Two pointing modes have been applied: (a) In the inertial mode, the spect...

The upper mesosphere and lower thermosphere of Mars (70–150 km) is of high interest because it is a region affected by climatological/meteorological events in the lower atmosphere and external solar forcing. However, only a few measurements are available at this altitude range. OI 557.7 nm dayglow emission has been detected at these altitudes by th...

Plain Language Summary The green and red oxygen emissions at 557.7 and 630 nm, respectively, are among the dominant spectral features of the terrestrial dayglow and aurora. Recently, the presence of the green emission was also observed in the Martian dayglow using the NOMAD/UVIS instrument on board the ExoMars Trace Gas Orbiter mission. The red lin...

Ionospheric conductance contributes to regulate the characteristics of the ionospheric current and the closure of the magnetosphere‐ionosphere circuit in the ionosphere. Measurements of Birkeland currents with the Juno magnetometer have indicated that they are statistically larger in the south. It has been suggested that these asymmetries may be th...

The oxygen emission at 557.7 nm is a ubiquitous component of the spectrum of the terrestrial polar aurora and the reason for its usual green colour1. It is also observed as a thin layer of glow surrounding the Earth near 90 km altitude in the dayside atmosphere2,3 but it has so far eluded detection in other planets. Here we report dayglow observati...

Ionospheric conductivity perpendicular to the magnetic field plays a crucial role in the electrical coupling between planetary magnetospheres and ionospheres. At Jupiter, it controls the flow of ionospheric current from above and the closure of the magnetosphere‐ionosphere circuit in the ionosphere. We use multispectral images collected with the Ul...

We report limb measurements of the oxygen dayglow emission at 297.2 nm performed during four Martian dust storms. The emission peak provides a good remote sensing tool to probe changes of the altitude of the 39 mPa pressure level for the first time during dust storms. We illustrate the time variation of these changes and compare them with the infra...

We apply a new technique to remotely sense the seasonal altitude variation of the 0.39μbar isobar level in this region. We present results from observations of airglow limb profiles collected during two Martian years with the Imaging UltraViolet Spectrograph (IUVS) onboard MAVEN. IUVS has collected tens of thousands of Martian airglow limb profiles...

We present comparisons of precipitating electron flux and auroral brightness measurements made during several Juno transits over Jupiter's auroral regions in both hemispheres. We extract from the ultraviolet spectrograph (UVS) spectral imager H2 emission intensities at locations magnetically conjugate to the spacecraft using the JRM09 model. We use...

We analyze two Martian years of dayglow measurements of the CO Cameron bands and the CO2⁺ ultraviolet doublet (UVD) at 298–299 nm with the Imaging UltraViolet Spectrograph on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter. We show that the altitude and the brightness of the two emissions peaks are strongly correlated, although dat...

We present an overview of two Martian Years (MYs) oxygen dayglow limb observations of the ultraviolet (UV) emissions at 130.4 and 135.6 nm. The data have been collected with the Imaging Ultraviolet Spectrograph (IUVS) instrument on board the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We use solar flux measurements of EUVM on board M...

The O(¹S) metastable atoms can radiatively relax by emitting airglow at 557.7 and 297.2 nm. The latter one has been observed with the Imaging Ultraviolet Spectrograph onboard the Mars Atmosphere and Volatile Evolution Mars orbiter since 2014. Limb profiles of the 297.2-nm dayglow have been collected near periapsis with a spatial resolution of 5 km...

We present a semi-automatic procedure to obtain fundamental physical parameters and distances of classical Be (CBe) stars, based on the Barbier-Chalonge-Divan (BCD) spectrophotometric system. Our aim is to apply this procedure to a large sample of CBe stars detected by the IPHAS photometric survey, to determine their fundamental physical parameters...

Our goal is to investigate the spiral structure of the Northern Galactic plane using as tracers the classical Be stars detected by INT Photometric H$\alpha$ Survey (IPHAS). IPHAS scans the $29^o<l<+215^o, -5^o<b<+5^o$ region in the $r$, $i$ and H$\alpha$ bands. Spectroscopic follow up has been done for the bright H$\alpha$ emitters. We have develop...

We present the results of our monitoring program to study the long-term variability of the Halpha line in high-mass X-ray binaries. We have carried out the most complete optical spectroscopic study of the global properties of high-mass X-ray binaries so far with the analysis of more than 1100 spectra of 20 sources. Our aim is to characterise the op...

Present X-ray missions are regularly discovering new X/gamma-ray sources. The identification of the counterparts of these high-energy sources at other wavelengths is important to determine their nature. In particular, optical observations are an essential tool in the study of X-ray binary populations in our Galaxy. The main goal of this work is to...