We have developed a one‐dimensional, diurnally averaged, photochemical model for Jupiter's stratosphere that couples photodissociation, chemical kinetics, vertical diffusion, and radiative transport. ...The predictions regarding the abundances and vertical profiles of hydrocarbon compounds are compared with observations from the Infrared Space Observatory (ISO) to better constrain the atmospheric composition, to better define the eddy diffusion coefficient profile, and to better understand the chemical reaction schemes that produce and destroy the observed constituents. From model‐data comparisons we determine that the C2H6 mole fraction on Jupiter is (4.0 ± 1.0) × 10−6 at 3.5 mbar and (2.7 ± 0.7) × 10−6 at 7 mbar, and the C2H2 mole fraction is (1.4 ± 0.8) × 10−6 at 0.25 mbar and (1.5 ± 0.4) × 10−7 at 2 mbar. The column densities of CH3C2H and C6H6 are (1.5 ± 0.4) × 1015 cm−2 and (8.0 ± 2) × 1014 cm−2, respectively, above 30 mbar. Using identical reaction lists, we also have developed photochemical models for Saturn, Uranus, and Neptune. Although the models provide good first‐order predictions of hydrocarbon abundances on the giant planets, our current chemical reaction schemes do not reproduce the relative abundances of C2Hx hydrocarbons. Unsaturated hydrocarbons like C2H4 and C2H2 appear to be converted to saturated hydrocarbons like C2H6 more effectively on Jupiter than on the other giant planets, more effectively than is predicted by the models. Further progress in our understanding of photochemistry at low temperatures and low pressures in hydrogen‐dominated atmospheres hinges on the acquisition of high‐quality kinetics data.
We present new astrometric and polarimetric observations of flares from Sgr A* obtained with GRAVITY, the near-infrared interferometer at ESO’s Very Large Telescope Interferometer (VLTI), bringing ...the total sample of well-covered astrometric flares to four and polarimetric flares to six. Of all flares, two are well covered in both domains. All astrometric flares show clockwise motion in the plane of the sky with a period of around an hour, and the polarization vector rotates by one full loop in the same time. Given the apparent similarities of the flares, we present a common fit, taking into account the absence of strong Doppler boosting peaks in the light curves and the EHT-measured geometry. Our results are consistent with and significantly strengthen our model from 2018. First, we find that the combination of polarization period and measured flare radius of around nine gravitational radii (9
R
g
≈ 1.5
R
ISCO
, innermost stable circular orbit) is consistent with Keplerian orbital motion of hot spots in the innermost accretion zone. The mass inside the flares’ radius is consistent with the 4.297 × 10
6
M
⊙
measured from stellar orbits at several thousand
R
g
. This finding and the diameter of the millimeter shadow of Sgr A* thus support a single black hole model. Second, the magnetic field configuration is predominantly poloidal (vertical), and the flares’ orbital plane has a moderate inclination with respect to the plane of the sky, as shown by the non-detection of Doppler-boosting and the fact that we observe one polarization loop per astrometric loop. Finally, both the position angle on the sky and the required magnetic field strength suggest that the accretion flow is fueled and controlled by the winds of the massive young stars of the clockwise stellar disk 1–5″ from Sgr A*, in agreement with recent simulations.
We report on Herschel/PACS observations of absorption lines of OH+, H2O+ and H3O+ in NGC 4418 and Arp 220. Excited lines of OH+ and H2O+ with Elower of at least 285 and ~200 K, respectively, are ...detected in both sources, indicating radiative pumping and location in the high radiation density environment of the nuclear regions. Abundance ratios OH+/H2O+ of 1−2.5 are estimated in the nuclei of both sources. The inferred OH+ column and abundance relative to H nuclei are (0.5−1) × 1016 cm-2 and ~ 2 × 10-8, respectively. Additionally, in Arp 220, an extended low excitation component around the nuclear region is found to have OH+/H2O+ ~ 5−10. H3O+ is detected in both sources with N(H3O+) ~ (0.5−2) × 1016 cm-2, and in Arp 220 the pure inversion, metastable lines indicate a high rotational temperature of ~500 K, indicative of formation pumping and/or hot gas. Simple chemical models favor an ionization sequence dominated by H+ → O+ → OH+ → H2O+ → H3O+, and we also argue that the H+ production is most likely dominated by X-ray/cosmic ray ionization. The full set of observations and models leads us to propose that the molecular ions arise in a relatively low density (≳104 cm-3) interclump medium, in which case the ionization rate per H nucleus (including secondary ionizations) is ζ > 10-13 s-1, a lower limit that is several × 102 times the highest current rate estimates for Galactic regions. In Arp 220, our lower limit for ζ is compatible with estimates for the cosmic ray energy density inferred previously from the supernova rate and synchrotron radio emission, and also with the expected ionization rate produced by X-rays. In NGC 4418, we argue that X-ray ionization due to an active galactic nucleus is responsible for the molecular ion production.
The broad-line region (BLR) of active galactic nuclei (AGNs) traces gas close to the central supermassive black hole (BH). Recent reverberation mapping (RM) and interferometric spectro-astrometry ...data have enabled detailed investigations of the BLR structure and dynamics as well as estimates of the BH mass. These exciting developments have motivated comparative investigations of BLR structures using different broad emission lines. In this work, we have developed a method to simultaneously model multiple broad lines of the BLR from a single-epoch spectrum. We applied this method to the five strongest broad emission lines (H α , H β , H γ , Pa β , and He I λ 5876) in the UV-to-near-IR spectrum of NGC 3783, a nearby Type I AGN that has been well studied by RM and interferometric observations. Fixing the BH mass to the published value, we fit these line profiles simultaneously to constrain the BLR structure. We find that the differences between line profiles can be explained almost entirely as being due to different radial distributions of the line emission. We find that using multiple lines in this way also enables one to measure some important physical parameters, such as the inclination angle and virial factor of the BLR. The ratios of the derived BLR time lags are consistent with the expectation of theoretical model calculations and RM measurements.
Herschel-PACS measurements of the rotational R(0) and R(1) HD lines in the atmospheres of Uranus and Neptune are analyzed to derive a D/H ratio with improved precision for the two planets. The ...derivation of the D/H ratio also includes previous measurements of the R(2) line with the Short Wavelength Spectrometer on board the Infrared Space Observatory (ISO). The available spectroscopic line information of the three rotational transitions is discussed and applied in the radiative transfer calculations. The best simultaneous fit of all three lines requires only a minor departure from the Spitzer temperature profile of Uranus and a departure limited to 2K from the Voyager temperature profile of Neptune (each time around the tropopause). The resulting and remarkably similar D/H ratios for Uranus and Neptune are found to be (4.4 ± 0.4) × 10-5 and (4.1 ± 0.4) × 10-5, respectively. Although the deuterium enrichment in the two atmospheres compared to the protosolar value is confirmed, it is found to be lower compared to previous analyses. Using interior models from the literature and assuming that complete mixing of the atmosphere and interior occured during the planets’ history, we derive a D/H in protoplanetary ices between (5.75–7.0) × 10-5 for Uranus and between (5.1–7.7) × 10-5 for Neptune. Conversely, adopting a cometary D/H for the protoplanetary ices between (15–30) × 10-5, we constrain the interior models of the two planets to have an ice mass fraction of 14–32%, i.e., the two planets are rock-dominated.
Context. The origin of water in the stratospheres of giant planets has been an outstanding question ever since its first detection by the Infrared Space Observatory some 20 years ago. Water can ...originate from interplanetary dust particles, icy rings and satellites, and large comet impacts. Analyses of Herschel Space Observatory observations have proven that the bulk of Jupiter’s stratospheric water was delivered by the Shoemaker-Levy 9 impacts in 1994. In 2006, the Cassini mission detected water plumes at the South Pole of Enceladus, which made the moon a serious candidate for Saturn’s stratospheric water. Further evidence was found in 2011 when Herschel demonstrated the presence of a water torus at the orbital distance of Enceladus that was fed by the moon’s plumes. Finally, water falling from the rings onto Saturn’s uppermost atmospheric layers at low latitudes was detected during the final orbits of Cassini’s end-of-mission plunge into the atmosphere. Aims. In this paper, we use Herschel mapping observations of water in Saturn’s stratosphere to identify its source. Methods. We tested several empirical models against the Herschel-HIFI and -PACS observations, which were collected on December 30, 2010, and January 2, 2011, respectively. Results. We demonstrate that Saturn’s stratospheric water is not uniformly mixed as a function of latitude, but peaks at the equator and decreases poleward with a Gaussian distribution. We obtain our best fit with an equatorial mole fraction 1.1 ppb and a half width at half maximum of 25°, when accounting for a temperature increase in the two warm stratospheric vortices produced by Saturn’s Great Storm of 2010–2011. Conclusions. This work demonstrates that Enceladus is the main source of Saturn’s stratospheric water.
Context. The GRAVITY beam-combiner at the Very Large Telescope Interferometer has recently made important contributions to many different fields of astronomy, from observations of the Galactic centre ...to the study of massive stars, young stellar objects, exoplanet atmospheres, and active galactic nuclei. These achievements were only made possible by the development of several key technologies, including the development of reliable and high-performance fringe trackers. These systems compensate for disturbances ranging from atmospheric turbulence to vibrations in the optical system, enabling long exposures and ensuring the stability of interferometric measurements. Aims. As part of the ongoing GRAVITY+ upgrade of the Very Large Telescope Interferometer infrastructure, we aim to improve the performance of the GRAVITY fringe tracker, and to enable its use by other instruments. Methods. We modified the group-delay controller to consistently maintain tracking in the white-light fringe, which is characterised by a minimum group delay. Additionally, we introduced a novel approach in which fringe-tracking is performed in the non-observable optical path length state-space using a covariance-weighted Kalman filter and an auto-regressive model of the disturbance. We outline this new state-space representation and the formalism we used to propagate the state vector and generate the control signal. While our approach is presented specifically in the context of GRAVITY/GRAVITY+, it can easily be adapted to other instruments or interfero-metric facilities. Results. We successfully demonstrate phase-delay tracking within a single fringe, with any spurious phase jumps detected and corrected in less than 100 ms. We also report a significant performance improvement, as shown by a reduction of ~30 to 40% in phase residuals, and a much better behaviour under sub-optimal atmospheric conditions. Compared to what was observed in 2019, the median residuals have decreased from 150 nm to 100 nm on the Auxiliary Telescopes and from 250 nm to 150 nm on the Unit Telescopes. Conclusions. The improved phase-delay tracking combined with white-light fringe tracking means that from now on, the GRAVITY fringe tracker can be used by other instruments operating in different wavebands. The only limitation remains the need for an adjustment of the optical path dispersion.
We have analyzed Titan observations performed by the Infrared Space Observatory (ISO) in the range 7–30 μm. The spectra obtained by three of the instruments on board the mission (the short wavelength ...spectrometer, the photometer, and the camera) were combined to provide new and more precise thermal and compositional knowledge of Titan’s stratosphere. With the high spectral resolution achieved by the SWS (much higher than that of the Voyager 1 IRIS spectrometer), we were able to detect and separate the contributions of most of the atmospheric gases present on Titan and to determine disk-averaged mole fractions. We have also tested existing vertical distributions for C
2H
2, HCN, C
2H
6, and CO
2 and inferred some information on the abundance of the first species as a function of altitude. From the CH
3D band at 1161 cm
−1 and for a CH
4 mole fraction assumed to be 1.9% in Titan’s stratosphere, we have obtained the monodeuterated methane-averaged abundance and retrieved a D/H isotopic ratio of 8.7−1.9+3.2 × 10
−5. We discuss the implications of this value with respect to current evolutionary scenarios for Titan. The ν
5 band of HC
3N at 663 cm
−1 was observed for the first time in a disk-averaged spectrum. We have also obtained a first tentative detection of benzene at 674 cm
−1, where the fit of the ISO/SWS spectrum at
R = 1980 is significantly improved when a constant mean mole fraction of 4 × 10
−10 of C
6H
6 is incorporated into the atmospheric model. This corresponds to a column density of ∼ 2 × 10
15 molecules cm
−2 above the 30-mbar level. We have also tested available vertical profiles for HC
3N and C
6H
6 and adjusted them to fit the data. Finally, we have inferred upper limits of a few 10
−10 for a number of molecules proposed as likely candidates on Titan (such as allene, acetonitrile, propionitrile, and other more complex gases).
The
Gaia
Multipeak (GMP) technique can be used to identify large numbers of dual or lensed active galactic nucleus (AGN) candidates at subarcsec separation, allowing us to study both multiple ...supermassive black holes (SMBHs) in the same galaxy and rare, compact lensed systems. The observed samples can be used to test the predictions of the models of SMBH merging when (1) the selection function of the GMP technique is known, and (2) each system has been classified as a dual AGN, a lensed AGN, or an AGN/star alignment. Here we show that the GMP selection is very efficient for separations above 0.15″ when the secondary (fainter) object has a magnitude
G
≲ 20.5. We present the spectroscopic classification of five GMP candidates using VLT/ERIS and Keck/OSIRIS and compare them with the classifications obtained from (a) the near-IR colors of seven systems obtained with LBT/LUCI, and (b) the analysis of the total spatially unresolved spectra. We conclude that colors and integrated spectra can already provide reliable classifications of many systems. Finally, we summarize the confirmed dual AGNs at
z
> 0.5 selected by the GMP technique, and compare this sample with other such systems from the literature, concluding that GMP can provide a large number of confirmed dual AGNs at separations below 7 kpc.
Aims. Our aim is to study the response of the gas-to-energetic processes associated with high-mass star formation and compare it with previously published studies on low- and intermediate-mass young ...stellar objects (YSOs) using the same methods. The quantified far-IR line emission and absorption of CO, H2O, OH, and O i reveals the excitation and the relative contribution of different atomic and molecular species to the gas cooling budget. Methods. Herschel/PACS spectra covering 55–190 μm are analyzed for ten high-mass star forming regions of luminosities Lbol ~ 104−106 L⊙ and various evolutionary stages on spatial scales of ~104 AU. Radiative transfer models are used to determine the contribution of the quiescent envelope to the far-IR CO emission. Results. The close environments of high-mass protostars show strong far-IR emission from molecules, atoms, and ions. Water is detected in all 10 objects even up to high excitation lines, often in absorption at the shorter wavelengths and in emission at the longer wavelengths. CO transitions from J = 14 − 13 up to typically 29 − 28 (Eu/kB ~ 580−2400 K) show a single temperature component with a rotational temperature of Trot ~ 300 K. Typical H2O excitation temperatures are Trot ~250 K, while OH has Trot ~ 80 K. Far-IR line cooling is dominated by CO (~75%) and, to a smaller extent, by O i (~20%), which becomes more important for the most evolved sources. H2O is less important as a coolant for high-mass sources because many lines are in absorption. Conclusions. Emission from the quiescent envelope is responsible for ~45–85% of the total CO luminosity in high-mass sources compared with only ~10% for low-mass YSOs. The highest− J lines (Jup ≥ 20) originate most likely in shocks, based on the strong correlation of CO and H2O with physical parameters (Lbol, Menv) of the sources from low- to high-mass YSOs. The excitation of warm CO described by Trot ~ 300 K is very similar for all mass regimes, whereas H2O temperatures are ~100 K high for high-mass sources compared with low-mass YSOs. The total far-IR cooling in lines correlates strongly with bolometric luminosity, consistent with previous studies restricted to low-mass YSOs. Molecular cooling (CO, H2O, and OH) is ~4 times greater than cooling by oxygen atoms for all mass regimes. The total far-IR line luminosity is about 10-3 and 10-5 times lower than the dust luminosity for the low- and high-mass star forming regions, respectively.
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