European Southern Observatory

About: European Southern Observatory is a facility organization based out in Garching bei München, Germany. It is known for research contribution in the topics: Galaxy & Stars. The organization has 3594 authors who have published 16157 publications receiving 823095 citations. The organization is also known as: The European Southern Observatory，ESO & ESO.

Lupus disks with faint CO isotopologues: low gas/dust or high carbon depletion?

Abstract: Context. An era has started in which gas and dust can be observed independently in protoplanetary disks, thanks to the recent surveys with the Atacama Large Millimeter/sub-millimeter Array (ALMA). The first near-complete high-resolution disk survey in both dust and gas in a single star-forming region has been carried out in Lupus, finding surprisingly low gas-to-dust ratios.Aims. The goal of this work is to fully exploit CO isotopologue observations in Lupus, comparing them with physical-chemical model results, in order to obtain gas masses for a large number of disks and compare gas and dust properties.Methods. We have employed the grid of physical-chemical models presented previously to analyze continuum and CO isotopologue (13 CO J = 3−2 and C18 O J = 3−2) observations of Lupus disks, including isotope-selective processes and freeze-out. We also employed the ALMA 13 CO-only detections to calculate disk gas masses for a total of 34 sources, which expands the sample of 10 disks reported earlier, where C18 O was also detected.Results. We confirm that overall gas-masses are very low, often lower than 1M J , when volatile carbon is not depleted. Accordingly, global gas-to-dust ratios are much lower than the expected interstellar-medium value of 100, which is predominantly between 1 and 10. Low CO-based gas masses and gas-to-dust ratios may indicate rapid loss of gas, or alternatively chemical evolution, for example, through sequestering of carbon from CO to more complex molecules, or carbon locked up in larger bodies.Conclusions. Current ALMA observations of 13 CO and continuum emission cannot distinguish between these two hypotheses. We have simulated both scenarios, but chemical model results do not allow us to rule out one of the two, pointing to the need to calibrate CO-based masses with other tracers. Assuming that all Lupus disks have evolved mainly as a result of viscous processes over the past few Myr, the previously observed correlation between the current mass accretion rate and dust mass implies a constant gas-to-dust ratio, which is close to 100 based on the observed M disk /Ṁ acc ratio. This in turn points to a scenario in which carbon depletion is responsible for the low luminosities of the CO isotopologue line.

Compact Starbursts in z ̃ 3-6 Submillimeter Galaxies Revealed by ALMA

Abstract: We report the source size distribution, as measured by ALMA millimetric continuum imaging, of a sample of 13 AzTEC-selected submillimeter galaxies (SMGs) at z(phot) similar to 3-6. Their infrared luminosities and star formation rates (SFRs) are L-IR similar to, 2-6 x 10(12) L-circle dot and similar to 200-600 M-circle dot yr(-1), respectively. The sizes of these SMGs range from 0 ''.10 to 0 ''.38, with a median of 0 ''.20(-0 '' 05)(+0 '' 03) (FWHM), corresponding to a median circularized effective radius (R-c,R-e) of 0.67(-0.14)(+0.13) kpc, comparable to the typical size of the stellar component measured in compact quiescent galaxies at, Z similar to 2 (cQGs)-R-e similar to 1 kpc. The median surface SFR density of our SMGs is 100(-26)(+42) M-circle dot yr(-1) kpc(-2) -1 comparable to that seen in local merger-driven (U)LIRGs rather than in extended disk galaxies at low and high redshifts. The discovery of compact starbursts in z greater than or similar to 3 SMGs strongly supports a massive galaxy formation scenario wherein z similar to 3-6 SMGs evolve into the compact stellar components of z similar to 2 cQGs. These cQGs are then thought to evolve into the most massive ellipticals in the local universe, mostly via dry mergers. Our results thus suggest that z greater than or similar to 3 SMGs are the likely progenitors of massive local ellipticals, via cQGs, meaning that we can now trace the evolutionary path of the most massive galaxies over a period encompassing similar to 90% of the age of the universe.

First radius measurements of very low mass stars with the VLTI

Abstract: We present 4 very low mass stars radii measured with the VLTI using the 2.2m VINCI test instrument. The observations were carried out during the commissioning of the 104-meter-baseline with two 8-meter-telescopes. We measure angular diameters of 0.7-1.5 mas with accuracies of 0.04-0.11 mas, and for spectral type ranging from M0V to M5.5V. We determine an empirical mass-radius relation for M dwarfs based on all available radius measurements. The observed relation agrees well with theoretical models at the present accuracy level, with possible discrepancy around 0.5-0.8 M that needs to be confirmed. In the near future, dozens of M dwarfs radii will be measured with 0.1-1% accuracy, with the VLTI, thanks to the improvements expected from the near infrared instrument AMBER. This will bring strong observational constraints on both atmosphere and interior physics.

The Spitzer c2d Survey of Large, Nearby, Interstellar Clouds. XI. Lupus Observed with IRAC and MIPS

Abstract: We present c2d Spitzer/IRAC observations of the Lupus I, III and IV dark clouds and discuss them in combination with optical and near-infrared and c2d MIPS data. With the Spitzer data, the new sample contains 159 stars, 4 times larger than the previous one. It is dominated by low- and very-low mass stars and it is complete down to M ≈ 0.1M⊙. We find 30-40% binaries with separations between 100 to 2000 AU with no apparent effect in the disk properties of the members. A large majority of the objects are Class II or Class III objects, with only 20 (12%) of Class I or Flat spectrum sources. The disk sample is complete down to “debris”-like systems in stars as small as M ≈ 0.2 M⊙ and includes sub-stellar objects with larger IR excesses. The disk fraction in Lupus is 70 – 80%, consistent with an age of 1 – 2 Myr. However, the young population contains 20% optically thick accretion disks and 40% relatively less flared disks. A growing variety of inner disk structures is found for larger inner disk clearings for

Three Hypervelocity White Dwarfs in Gaia DR2: Evidence for Dynamically Driven Double-degenerate Double-detonation Type Ia Supernovae

Abstract: Double detonations in double white dwarf (WD) binaries undergoing unstable mass transfer have emerged in recent years as one of the most promising Type Ia supernova (SN Ia) progenitor scenarios. One potential outcome of this "dynamically driven double-degenerate double-detonation" (D6) scenario is that the companion WD survives the explosion and is flung away with a velocity equal to its >1000 km s−1 pre-SN orbital velocity. We perform a search for these hypervelocity runaway WDs using Gaia's second data release. In this paper, we discuss seven candidates followed up with ground-based instruments. Three sources are likely to be some of the fastest known stars in the Milky Way, with total Galactocentric velocities between 1000 and 3000 km s−1, and are consistent with having previously been companion WDs in pre-SN Ia systems. However, although the radial velocity of one of the stars is >1000 km s−1, the radial velocities of the other two stars are puzzlingly consistent with 0. The combined five-parameter astrometric solutions from Gaia and radial velocities from follow-up spectra yield tentative 6D confirmation of the D6 scenario. The past position of one of these stars places it within a faint, old SN remnant, further strengthening the interpretation of these candidates as hypervelocity runaways from binary systems that underwent SNe Ia.