101 research outputs found
Orbital parameters estimation for compact binary stars
Most stars in the Galaxy are found in multiple systems of two or more stars orbiting together. Two stars orbiting around their centre of mass are called binary stars. In close binary stars, the evolution of one star affects its companion and evolutionary expansion of one star allows for mass exchange between the components. In most cases, the material from the less massive star forms an accretion disc around the heavier companion that has evolved into a compact stellar remnant, the final state of stellar evolution. We call these systems compact binary stars (CBs). The study of CBs is key to the development of two fundamental phenomena: accretion and evolution of binary stars.
Statistical information on CBs can be deduced by extracting common properties and characteristic system parameter distributions from observed data. But, despite being fundamental for a wide range of astronomical phenomena, our comprehension of their formation and evolution is still poor, mainly because of the limited knowledge of crucial orbital parameters. This lack of reliable orbital parameters estimation is mainly due to observational handicaps, namely, the accretion disc outshines the system components. Astronomers have developed different techniques to overcome this, but are often very dependant of the signal to noise ratio of the data or are only able to obtain via target of opportunity programs (wait until the target is brighter).
The focus of this work is to test and develop techniques, based on indirect imaging methods, that can overcome the main observational handicaps to estimate orbital parameters of CBs. We combine these techniques with the exploitation of more “exotic” emission lines that trace the irradiated face of the donor star, namely Ca II NIR triplet and the Bowen blend. We made use of empirical properties of Doppler tomography to estimate the values of the phase zero Á0 and the velocity of the irradiated face of the secondary star (Kem). We then used synthetic models accounting for an irradiated secondary to fit our measured Kem and perform a K-correction to derive the radial velocity of the secondary K2. To derive K1, we used the centre of symmetry technique, testing its validity among several emission lines and the stability of the results depending on the selected area. Having strong constraints for K1 and K2, we find estimates for the mass ratio q. Furthermore, we developed a variation from the Doppler tomography secondary emission method to constrain the value of the systemic velocity ƴ. We derive meaningful uncertainties of these parameters with the bootstrap technique.
Using these techniques, we have successfully set dynamical constraints on the radial velocities of the binary components of CBs and derived fundamental orbital parameters, including the mass ratio, using basic properties of Doppler tomography
Using large spectroscopic surveys to test the double degenerate model for Type Ia supernovae
An observational constraint on the contribution of double degenerates to Type Ia supernovae requires multiple radial velocity measurements of ideally thousands of white dwarfs. This is because only a small fraction of the double degenerate population is massive enough, with orbital periods short enough, to be considered viable Type Ia progenitors. We show how the radial velocity information available from public surveys such as the Sloan Digital Sky Survey can be used to pre-select targets for variability, leading to a 10-fold reduction in observing time required compared to an unranked or random survey. We carry out Monte Carlo simulations to quantify the detection probability of various types of binaries in the survey and show that this method, even in the most pessimistic case, doubles the survey size of the largest survey to date (the SPY Survey) in less than 15 per cent of the required observing time. Our initial follow-up observations corroborate the method, yielding 15 binaries so far (eight known and seven new), as well as orbital periods for four of the new binaries
Tomography of X-ray Nova Muscae 1991: Evidence for ongoing mass transfer and stream-disc overflow
We present a spectroscopic analysis of the black hole binary Nova Muscae 1991
in quiescence using data obtained in 2009 with MagE on the Magellan Clay
telescope and in 2010 with IMACS on the Magellan Baade telescope at the Las
Campanas Observatory. Emission from the disc is observed in H alpha, H beta and
Ca II (8662 A). A prominent hotspot is observed in the Doppler maps of all
three emission lines. The existence of this spot establishes ongoing mass
transfer from the donor star in 2009-2010 and, given its absence in the
1993-1995 observations, demonstrates the presence of a variable hotspot in the
system. We find the radial distance to the hotspot from the black hole to be
consistent with the circularization radius. Our tomograms are suggestive of
stream-disc overflow in the system. We also detect possible Ca II (8662 A)
absorption from the donor star.Comment: 10 pages, 11 figures, 1 table. Accepted for publication in MNRA
Close companions around young stars
Multiplicity is a fundamental property that is set early during stellar
lifetimes, and it is a stringent probe of the physics of star formation. The
distribution of close companions around young stars is still poorly constrained
by observations. We present an analysis of stellar multiplicity derived from
APOGEE-2 spectra obtained in targeted observations of nearby star-forming
regions. This is the largest homogeneously observed sample of high-resolution
spectra of young stars. We developed an autonomous method to identify double
lined spectroscopic binaries (SB2s). Out of 5007 sources spanning the mass
range of 0.05--1.5 \msun, we find 399 binaries, including both RV
variables and SB2s. The mass ratio distribution of SB2s is consistent with a
uniform for . The period
distribution is consistent with what has been observed in close binaries (
AU) in the evolved populations. Three systems are found to have 0.1,
with a companion located within the brown dwarf desert. There are not any
strong trends in the multiplicity fraction (MF) as a function of cluster age
from 1 to 100 Myr. There is a weak dependence on stellar density, with
companions being most numerous at stars/pc, and
decreasing in more diffuse regions. Finally, disk-bearing sources are deficient
in SB2s (but not RV variables) by a factor of 2; this deficit is
recovered by the systems without disks. This may indicate a quick dispersal of
disk material in short-period equal mass systems that is less effective in
binaries with lower .Comment: 25 pages, 20 figures. Accepted to A
The chemical properties of the Milky Way's on-bar and off-bar regions: evidence for inhomogeneous star formation history in the bulge
Numerous studies of integrated starlight, stellar counts, and kinematics have
confirmed that the Milky Way is a barred galaxy. However, far fewer studies
have investigated the bar's stellar population properties, which carry valuable
independent information regarding the bar's formation history. Here we conduct
a detailed analysis of chemical abundance distributions ([Fe/H] and [Mg/Fe]) in
the on-bar and off-bar regions to study the azimuthal variation of star
formation history (SFH) in the inner Galaxy. We find that the on-bar and
off-bar stars at Galactocentric radii 3 5 kpc have remarkably
consistent [Fe/H] and [Mg/Fe] distribution functions and [Mg/Fe]--[Fe/H]
relation, suggesting a common SFH shared by the long bar and the disc. In
contrast, the bar and disc at smaller radii (2 3 kpc) show
noticeable differences, with relatively more very metal-rich ([Fe/H]~0.4) stars
but fewer solar abundance stars in the bar. Given the three-phase star
formation history proposed for the inner Galaxy in Lian et al. (2020b), these
differences could be explained by the off-bar disc having experienced either a
faster early quenching process or recent metal-poor gas accretion. Vertical
variations of the abundance distributions at small suggest a wider
vertical distribution of low- stars in the bar, which may serve as
chemical evidence for vertical heating through the bar buckling process. The
lack of such vertical variations outside the bulge may then suggest a lack of
vertical heating in the long bar.Comment: 10 pages, 5 figures. MNRAS in pres
Revealing the Chemical Structure of the Magellanic Clouds with APOGEE. III. Abundance Gradients of the Small Magellanic Cloud
We determine radial- and age-abundance gradients of the Small Magellanic
Cloud (SMC) using spectra of 2,062 red giant branch (RGB) field stars observed
by SDSS-IV / APOGEE-2S. With coverage out to 9 kpc in the SMC, these data
taken with the high resolution () APOGEE -band spectrograph
afford the opportunity to measure extensive radial gradients for as many as 24
abundance ratios. The SMC is found to have an overall metallicity gradient of
0.0546 0.0043 dex/kpc. Ages are calculated for every star to explore
the evolution of the different abundance gradients. As a function of age, many
of the gradients show a feature 3.66--5.58 Gyr ago, which is especially
prominent in the [X/H] gradients. Initially many gradients flatten until about
5.58 Gyr ago, but then steepen in more recent times. We previously
detected similar evolutionary patterns in the Large Magellanic Cloud (LMC)
which are attributed to a recent interaction between the LMC and SMC. It is
inferred that the feature in the SMC gradients was caused by the same
interaction. The age-[X/Fe] trends, which track average [X/Fe] over time, are
flat, demonstrating a slow enrichment history for the SMC. When comparing the
SMC gradients to the LMC and MW, normalized to disk scale length
(), the [X/Fe] and [X/Mg] gradients are similar, but there is a
dichotomy between the dwarfs and the Milky Way (MW) for the [X/H] gradients.
The median MW [X/H] gradient around 0.125 dex/ whilst the Clouds
have gradients of about 0.075 dex/.Comment: 27 pages, 22 figures, and 11 table
Revealing the Chemical Structure of the Magellanic Clouds with APOGEE. II. Abundance Gradients of the Large Magellanic Cloud
We present the abundance gradients of the Large Magellanic Cloud (LMC) for 25
elemental abundance ratios and their respective temporal evolution as well as
age-[X/Fe] trends using 6130 LMC field red giant branch (RGB) stars observed by
SDSS-IV / APOGEE-2S. APOGEE is a high resolution ( 22,500) -band
spectroscopic survey that gathered data on the LMC with broad radial and
azimuthal coverage out to 10\degr. The calculated overall metallicity
gradient of the LMC with no age binning is 0.0380 0.0022 dex/kpc. We
also find that many of the abundance gradients show a U-shaped trend as
functions of age. This trend is marked by a flattening of the gradient but then
a general steepening at more recent times. The extreme point at which all these
gradients (with the U-shaped trend) begin to steepen is 2 Gyr ago. In
addition, some of the age-[X/Fe] trends show an increase starting a few Gyr
before the extreme point in the gradient evolutions. A subset of the age-[X/Fe]
trends also show maxima concurrent with the gradients' extreme points, further
pinpointing a major event in the history of the LMC 2 Gyr ago. This time
frame is consistent with a previously proposed interaction between the
Magellanic Clouds suggesting that this is most likely the cause of the distinct
trend in the gradients and age-[X/Fe] trends.Comment: 25 pages, 19 figures, and 10 table
VLT, GROND and Danish telescope observations of transits in the TRAPPIST-1 system
Funding: UGJ acknowledges funding from the Novo Nordisk Foundation Interdisciplinary Synergy Programme grant no. NNF19OC0057374 and from the European Union H2020-MSCA-ITN-2019 under Grant no. 860470 (CHAMELEON). NP’s work was supported by Fundação para a Ciência e a Tecnologia (FCT) through the research grants UIDB/04434/2020 and UIDP/04434/2020. PLP was partly funded by Programa de Iniciación en Investigación-Universidad de Antofagasta, INI-17-03.TRAPPIST-1 is an ultra-cool dwarf that hosts seven known transiting planets. We present photometry of the system obtained using three telescopes at ESO La Silla (the Danish 1.54-m telescope and the 2.2-m MPI telescope) and Paranal (Unit Telescope 1 of the Very Large Telescope). We obtained 18 light curves from the Danish telescope, eight from the 2.2-m and four from the VLT. From these we measure 25 times of mid-transit for four of the planets (b, c, f, g). These light curves and times of mid-transit will be useful in determining the masses and radii of the planets, which show variations in their transit times due to gravitational interactions.PostprintPeer reviewe
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