Silicon immersion gratings and their spectroscopic applications

We study the Roman sensitivity to exoplanets in the Habitable Zone (HZ). The Roman efficiency for detecting habitable planets is maximized for three classes of planetary microlensing events with close caustic topologies. (a) The events with the lens distances of Dl ≳ 7 kpc, the host lens masses of $M_{\rm h}\gtrsim 0.6\, {\rm M}_{\odot }$. By assuming Jupiter-mass planets in the HZs, these events have q ≲ 0.001 and d ≳ 0.17 (q is their mass ratio and d is the projected planet-host distance on the sky plane normalized to the Einstein radius). The events with primary lenses, $M_{\rm h} \lesssim 0.1 \, {\rm M}_{\odot }$, while their lens systems are either (b) close to the observer with Dl ≲ 1 kpc or (c) close to the Galactic bulge, Dl ≳ 7 kpc. For Jupiter-mass planets in the HZs of the primary lenses, the events in these two classes have q ≳ 0.01, d ≲ 0.04. The events in the class (a) make larger caustics. By simulating planetary microlensing events detectable by Roman, we conclude that the Roman efficiencies for detecting Earth- and Jupiter-mass planets in the Optimistic HZs (OHZs, which is the region between [0.5, 2] au around a Sun-like star) are 0.01 and $5{{\ \rm per\ cent}}$, respectively. If we assume that one exoplanet orbits each microlens in microlensing events detectable by Roman (i.e. ∼27 000), this telescope has the potential to detect 35 exoplanets with the projected planet-host distances in the OHZs with only one having a mass ≲10M⊕. According to the simulation, 27 of these exoplanets are actually in the OHZs.

The detection of habitable worlds is one of humanity’s greatest endeavors. Thus far, astrobiological studies have shown that one of the most critical components for allowing life to develop is liquid water. Its chemical properties and its capacity to dissolve and, hence, transport other substances makes this constituent a key piece in this regard. As a consequence, looking for life as we know it is directly related to the search for liquid water. For a remote detection of life in distant planetary systems, this essentially means looking for planets in the so-called habitable zone. In this sense, K-dwarf stars are the perfect hosts to search for planets in this range of distances. Contrary to G-dwarfs, the habitable zone is closer, thus making planet detection easier using transit or radial velocity techniques. Contrary to M-dwarfs, stellar activity is on a much smaller scale, hence, it has a smaller impact in terms of both the detectability and the true habitability of the planet. Also, K-dwarfs are the quietest in terms of oscillations, and granulation noise. In spite of this, there is a dearth of planets in the habitable zone of K-dwarfs due to a lack of observing programs devoted to this parameter space. In response to a call for legacy programs of the Calar Alto observatory, we have initiated the first dedicated and systematic search for habitable planets around these stars: K-dwarfs Orbited By habitable Exoplanets (KOBE). This survey is monitoring the radial velocity of 50 carefully pre-selected K-dwarfs with the CARMENES instrument over five semesters, with an average of 90 data points per target. Based on planet occurrence rates convolved with our detectability limits, we expect to find 1.68 ± 0.25 planets per star in the KOBE sample. Furthermore, in half of the sample, we expect to find one of those planets within the habitable zone. Here, we describe the motivations, goals, and target selection for the project as well as the preliminary stellar characterization.

‘The definitive version is available at www3.interscience.wiley.com Copyright Royal Astronomical Society

We use moderate-resolution spectra of nearby late K and M dwarf stars with parallaxes and interferometrically determined radii to refine their effective temperatures, luminosities, and metallicities. We use these revised values to calibrate spectroscopic techniques to infer the fundamental parameters of more distant late-type dwarf stars. We demonstrate that, after masking out poorly modeled regions, the newest version of the PHOENIX atmosphere models accurately reproduce temperatures derived bolometrically. We apply methods to late-type hosts of transiting planet candidates in the Kepler field, and calculate effective temperature, radius, mass, and luminosity with typical errors of 57 K, 7%, 11%, and 13%, respectively. We find systematic offsets between our values and those from previous analyses of the same stars, which we attribute to differences in atmospheric models utilized for each study. We investigate which of the planets in this sample are likely to orbit in the circumstellar habitable zone. We determine that four candidate planets (KOI 854.01, 1298.02, 1686.01, and 2992.01) are inside of or within 1-sigma of a conservative definition of the habitable zone, but that several planets identified by previous analyses are not (e.g. KOI 1422.02 and KOI 2626.01). Only one of the four habitable-zone planets is Earth sized, suggesting a downward revision in the occurrence of such planets around M dwarfs. These findings highlight the importance of measuring accurate stellar parameters when deriving parameters of their orbiting planets.

Structural and spectroscopic studies of alkali-metal exchanged stilbites

With the discovery of rocky planets in the temperate habitable zone (HZ) of the close-by cool star TRAPPIST-1, the question of whether such planets could harbour life arises. Habitable planets around red dwarf stars can orbit in radiation environments that can be life-sterilizing. Ultraviolet (UV) flares from these stars are more frequent and intense than solar flares. Additionally, their temperate HZs are closer to the star. Here we present UV surface environment models for TRAPPIST-1’s HZ planets and explore the implications for life. TRAPPIST-1 has high X-ray/extreme-ultraviolet activity, placing planetary atmospheres at risk from erosion. If a dense Earth-like atmosphere with a protective ozone layer existed on planets in the HZ of TRAPPIST-1, UV surface environments would be similar to the present-day Earth. However, an eroded or an anoxic atmosphere would allow more UV to reach the surface, making surface environments hostile even to highly UV tolerant terrestrial extremophiles. If future observations detect ozone in the atmospheres of any of the planets in the HZ of TRAPPIST-1, these would be interesting targets for the search for surface life. We anticipate our assay to be a starting point for in-depth exploration of stellar and atmospheric observations of the TRAPPIST-1 planets to constrain their UV surface habitability.

Highly qualitative indium tin oxide (ITO) films were deposited by reactive dc-sputter technique on glass and quartz substrates. Both pure H2O vapor and pure O2 have been used as reactive sputtering atmosphere. The optical constants refractive index and absorption coefficient were calculated from reflection and transmission spectra in the infrared (IR) region. Using the Drude theory the electrical parameters free carrier concentration and carrier mobility of the ITO-films were contactless determined from IR reflection spectra. The dc-H2O-sputtered ITO-films show improved optical and electrical properties. For application as transparent window material they distinguish by high visual (VIS) transmittance and high IR- reflectance. Moreover these ITO-films show a high free carrier concentration of N equals 6 X 1020 cm-3 directly after deposition compared with N equals 4 X 1020 cm-3 for dc-O2-sputtered ITO-films after thermal annealing. The differences between optical and electrical properties of de-O2- and dc-H2O-sputtered ITO-films are discussed in regard to their crystal structure and surface morphology.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

NC 3NC: a combined millimetre-wave spectroscopic and ab initio investigation

Recent studies have revealed that, in addition to insolation, the CO2 degassing rate is an important limiting factor on the resulting climate of Earth-like The CO2 degassing rate should change with time owing to the thermal evolution of planetary interiors. Here we use a mantle degassing model coupled with a parameterized convection model to estimate the climatic evolution of Earth-like planets with different masses and distances from their central stars. The CO2 degassing rate decreases monotonically with time owing to the decreasing mantle temperature. The CO2 degassing rate for large planets is higher than that for small planets because the interiors of large planets are hotter than those of small However, the effects arising from the difference in CO2 degassing rate could be compensated by the difference in the silicate weathering rate derived from the difference in the surface area among planets with different size and with a similar land/sea ratio as the Earth. These results indicate that most of the Earth-like planets in the outer regions of the habitable zones (HZs) of old planetary systems are in the climate mode (i.e., oscillating between and warm states), irrespective of planetary mass. Because the state lasts much longer than the warm climate state, Earth-like planets in HZs around old stars would statistically be observed as snowball planets.

The initial mass function describes the distribution of masses for a population of stars and substellar objects when they are born. It defines the evolution of a population of stars and provides constrains on the star formation theory. The determination of the initial mass function in the substellar regime is still an open question in Astrophysics. Brown dwarfs do not have enough mass to sustain hydrogen fusion. As a consequence, mass and age are degenerate for these objects. An older high mass object may be indistinguishable from a younger low mass object. In this PhD thesis, through the characterization of brown dwarfs using several observational methods, I work towards solving the general problem of constraining the substellar initial mass function. In my first project, I calculated trigonometric parallaxes of a sample of six cool brown dwarfs. I determined the luminosity for our objects and I found that one of them might be a brown dwarf binary. In my second project, I confirmed the youth of seven brown dwarfs (ages between 1 and 150 Myr) using spectroscopic data. In the last project of this PhD thesis, I aimed to refine the brown dwarf binary fraction using spectroscopic data in the optical and in the near infrared for 22 brown dwarfs. I found six new brown dwarf binary candidates, two of them were previously known. The determination of distances, ages and the refinement of the brown dwarf binary fraction in this PhD thesis contribute to the determination of the initial mass function. In the next years, the Gaia satellite, the JamesWebb Space Telescope and the E-ELT will provide new data, allowing the discovery of new brown dwarf binaries, the constraining of atmospheric and evolutionary models, and the refinement of the intial mass function.

A flexible electrochromic device with variable infrared emissivity based on W18O49 nanowire cathode and MXene infrared transparent conducting electrode

The <i>habitable zone</i> of a star is the range of distances from it where temperatures allow the existence of water in its liquid state on the surface of a planet with sufficient atmospheric pressure. This chapter is an overview of a study meant to identify potentially habitable exoplanets using actual data available online from NASA’s Kepler Mission.

Formation of terrestrial planets in Habitable Zones around M stars

Kepler 186f: First Earth-Sized Planet in Habitable Zone

The current exoplanet database includes 5454 confirmed and candidate planets observed with the Kepler mission. We find 932 planet pairs from which we extract distance and orbital period ratios. While earlier studies used a logarithmic spacing, which lacks a physical model, we employ here the theory of harmonic orbit resonances, which contains quantized ratios instead, to explain the observed planet distance ratios and to predict undetected exoplanets. We find that the most prevailing harmonic ratios are (2:1), (3:2), and (5:3) in 73% of the cases, while alternative harmonic ratios of (5:4), (4:3), (5:2), and (3:1) occur in the other 27% of the cases. Our orbital predictions include 171 exoplanets, 2 Jupiter moons, 1 Saturn moon, 3 Uranus moons, and 4 Neptune moons. The accuracy of the predicted planet distances amounts to a few percent, which fits the data significantly better than the logarithmic spacing. This information may be useful for targeted exoplanet searches with Kepler data and to estimate the number of live-carrying planets in habitable zones.