We introduce the Ophiuchus DIsc Survey Employing ALMA (ODISEA), a project aiming to study the entire population of Spitzer-selected protoplanetary discs in the Ophiuchus Molecular Cloud (∼300 ...objects) from both millimetre continuum and CO isotopologues data. Here we present 1.3 mm/230 GHz continuum images of 147 targets at 0.2 arcsec (28 au) resolution and a typical rms of 0.15 mJy. We detect a total of 133 discs, including the individual components of 11 binary systems and 1 triple system. 60 of these discs are spatially resolved. We find clear substructures (inner cavities, rings, gaps, and/or spiral arms) in eight of the sources and hints of such structures in another four discs. We construct the disc luminosity function for our targets and perform preliminary comparisons to other regions. A simple conversion between flux and dust mass (adopting standard assumptions) indicates that all discs detected at 1.3 mm are massive enough to form one or more rocky planets. In contrast, only ∼50 discs (∼1/3 of the sample) have enough mass in the form of dust to form the canonical 10 M⊕ core needed to trigger runaway gas accretion and the formation of gas giant planets, although the total mass of solids already incorporated into bodies larger than cm scales is mostly unconstrained. The distribution in continuum disc sizes in our sample is heavily weighted towards compact discs: most detected discs have radii < 15 au, while only 23 discs ({∼ }15{{ per cent}} of the targets) have radii > 30 au.
The enigmatic binary system HD 5980 Hillier, D John; Koenigsberger, Gloria; Nazé, Yaël ...
Monthly notices of the Royal Astronomical Society,
06/2019, Letnik:
486, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
The Small Magellanic Cloud multiple system HD 5980 contains a luminous blue variable (LBV) that underwent a major eruption in 1994, and whose current spectrum is that of a hydrogen-rich ...Wolf–Rayet (WR) star. Since the eruption, the wind mass-loss rate has been declining while wind speeds have been steadily increasing. Observations obtained in 2014 when Star A (the LBV) eclipses Star B indicate that the fitted mass-loss rate and luminosity have reached the lowest values ever determined for such spectra: $\dot{M}$ = 4.5 × 10−5$\mathrm{M}_\odot \, \hbox{yr}^{-1}$, L = 1.7 × 106 L⊙. In addition, the radius of the LBV’s continuum-emitting region is similar to that derived from the eclipse light curves of the late 1970s. Hence, it appears to have attained a similar ‘low’ state to that of the late 1970s. While a good fit to the emission spectrum is obtained using a cmfgen model, there are discrepancies in the UV. In particular, the extent of the observed absorption profiles is ∼1000 km s−1 greater than predicted by the emission-line intensities. Further, HST UV observations obtained in 2016, when Star A is eclipsed by Star B, show unusual P Cygni profiles that are not easily explained. Surprisingly the 2016 emission-line spectrum is similar to that at the opposite eclipse obtained in 2014. The complex UV profiles are likely to arise as a consequence of the dynamics of the wind–wind collision and radiative braking, both of which will cause significant departures from spherical symmetry, and have a strong orbital phase dependence. However, other scenarios, such as intrinsically aspherical winds, cannot be ruled out.
We present extensive spectroscopic and photometric monitoring of two famous and currently highly active luminous blue variables (LBVs) in the Large Magellanic Cloud (LMC), together with more limited ...coverage of three further, lesser known members of the class. R127 was discovered as an Ofpe/WN9 star in the 1970s but entered a classical LBV outburst in or about 1980 that is still in progress, thus enlightening us about the minimum state of such objects. R71 is currently the most luminous star in the LMC and continues to provide surprises, such as the appearance of Ca ii emission lines, as its spectral type becomes unprecedentedly late. Most recently, R71 has developed inverse P Cyg profiles in many metal lines. The other objects are as follows: HDE 269582, now a "second R127" that has been followed from Ofpe/WN9 to A type in its current outburst; HDE 269216, which changed from late B in 2014 to AF in 2016, its first observed outburst; and R143 in the 30 Doradus outskirts. The light curves and spectroscopic transformations are correlated in remarkable detail and their extreme reproducibility is emphasized, both for a given object and among all of them. It is now believed that some LBVs proceed directly to core collapse. One of these unstable LMC objects may thus oblige in the near future, teaching us even more about the final stages of massive stellar evolution.
New spectroscopic observations of the LBV/WR multiple system HD 5980 in the Small Magellanic Cloud are used to address the question of the masses and evolutionary status of the two very luminous ...stars in the 19.3 day eclipsing binary system. Two distinct components of the N V4944 Angstrom line are detected in emission and their radial velocity variations are used to derive masses of 61 and 66 M sub(middot in circle), under the assumption that binary interaction effects on this atomic transition are negligible. We propose that this binary system is the product of quasi-chemically homogeneous evolution with little or no mass transfer. Thus, both of these binary stars may be candidates for gamma-ray burst progenitors or even pair instability supernovae. Analysis of the photospheric absorption lines belonging to the third-light object in the system confirm that it consists of an O-type star in a 96.56 day eccentric orbit (e = 0.82) around an unseen companion. The 5:1 period ratio and high eccentricities of the two binaries suggest that they may constitute a hierarchical quadruple system.
ABSTRACT
Pristine_183.6849 + 04.8619 (P1836849) is an extremely metal-poor (Fe/H = −3.3 ± 0.1) star on a prograde orbit confined to the Galactic disc. Such stars are rare and may have their origins ...in protogalactic fragments that formed the early Milky Way, in low-mass satellites accreted later, or forming in situ in the Galactic plane. Here, we present a chemo-dynamical analysis of the spectral features between 3700−11 000 Å from a high-resolution spectrum taken during Science Verification of the new Gemini High-resolution Optical SpecTrograph. Spectral features for many chemical elements are analysed (Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Ni), and valuable upper limits are determined for others (C, Na, Sr, Ba). This main sequence star exhibits several rare chemical signatures, including (i) extremely low metallicity for a star in the Galactic disc, (ii) very low abundances of the light α-elements (Na, Mg, Si) compared to other metal-poor stars, and (iii) unusually large abundances of Cr and Mn, where Cr, Mn/FeNLTE > +0.5. A comparison to theoretical yields from supernova models suggests that two low-mass Population III objects (one 10 M⊙ supernova and one 17 M⊙ hypernova) can reproduce the abundance pattern well (reduced χ2 < 1). When this star is compared to other extremely metal-poor stars on quasi-circular, prograde planar orbits, differences in both chemistry and kinematics imply there is little evidence for a common origin. The unique chemistry of P1836849 is discussed in terms of the earliest stages in the formation of the Milky Way.
We present ALMA 1.3 mm continuum observations at (25 au) resolution of Elias 2-24, one of the largest and brightest protoplanetary disks in the Ophiuchus Molecular Cloud, and we report the presence ...of three partially resolved concentric gaps located at ∼20, 52, and 87 au from the star. We perform radiative transfer modeling of the disk to constrain its surface density and temperature radial profile and place the disk structure in the context of mechanisms capable of forming narrow gaps such as condensation fronts and dynamical clearing by actively forming planets. In particular, we estimate the disk temperature at the locations of the gaps to be 23, 15, and 12 K (at 20, 52, and 87 au, respectively), very close to the expected snowlines of CO (23-28 K) and N2 (12-15 K). Similarly, by assuming that the widths of the gaps correspond to 4-8× the Hill radii of forming planets (as suggested by numerical simulations), we estimate planet masses in the range of , , and for the inner, middle, and outer gap, respectively. Given the surface density profile of the disk, the amount of "missing mass" at the location of each one of these gaps (between 4 and 20 ) is more than sufficient to account for the formation of such planets.
We present results of our ongoing observing program on search and studies of massive stars (O type) in binary systems in our neighbour galaxies, the Magellanic Clouds. Radial velocity orbits are ...presented for two new binaries, one in the Small Magellanic Cloud and another in the Large Magellanic Cloud.
Analysis of spectral line profile variations observed over 6 decades in the Wolf-Rayet system HD 5980 lead to the conclusion that Star A, the variable member of the system, has always dominated the ...wind collision zone (WCZ), contrary to suggestions that before 1994 the stronger wind belonged to its close companion, Star B. The observed variations are caused by a combination of physical occultations, wind eclipses and emission and absorption originating in the WCZ. The effects caused by the leading WCZ branch, which folds around Star B, are clearly seen as it crosses our line of sight to Star A during the secondary eclipse. These effects can inform on the WCZ velocity and density structures. We speculate that differences in line profiles at the same orbital phase but at different epochs may be linked to changes in the WCZ radiative properties. The 2017-2020 spectra indicate that HD 5980 was in a higher activity state than during 2010-2015.
Over the past 40 years, the massive luminous blue variable/Wolf-Rayet system HD 5980 in the Small Magellanic Cloud (SMC) has undergone a long-term S Doradus-type variability cycle and two brief and ...violent eruptions in 1993 and 1994. In this paper we analyze a collection of UV and optical spectra obtained between 1979 and 2009 and perform CMFGEN model fits to spectra of 1994, 2000, 2002, and 2009. The results are as follows: (1) the long-term S Dor-type variability is associated with changes of the hydrostatic radius; (2) the 1994 eruption involved changes in its bolometric luminosity and wind structure; (3) the emission-line strength, the wind velocity, and the continuum luminosity underwent correlated variations in the sense that a decreasing V {infinity} is associated with increasing emission line and continuum levels; and (4) the spectrum of the third star in the system (Star C) is well fit by a T eff = 32 K model atmosphere with SMC chemical abundances. For all epochs, the wind of the erupting star is optically thick at the sonic point and is thus driven mainly by the continuum opacity. We speculate that the wind switches between two stable regimes driven by the 'hot' (during the eruption) and the 'cool' (post-eruption) iron opacity bumps as defined by Lamers & Nugis and Grafener & Hamann, and thus the wind may undergo a bi-stability jump of a different nature from that which occurs in OB stars.
PDF
