27 research outputs found
A new method of measuring center-of-mass velocities of radially pulsating stars from high-resolution spectroscopy
We present a radial velocity analysis of 20 solar neighborhood RR Lyrae and 3
Population II Cepheids variables. We obtained high-resolution, moderate-to-high
signal-to-noise ratio spectra for most stars and obtained spectra were covering
different pulsation phases for each star. To estimate the gamma
(center-of-mass) velocities of the program stars, we use two independent
methods. The first, `classic' method is based on RR Lyrae radial velocity curve
templates. The second method is based on the analysis of absorption line
profile asymmetry to determine both the pulsational and the gamma velocities.
This second method is based on the Least Squares Deconvolution (LSD) technique
applied to analyze the line asymmetry that occurs in the spectra. We obtain
measurements of the pulsation component of the radial velocity with an accuracy
of 3.5 km s. The gamma velocity was determined with an accuracy
10 km s, even for those stars having a small number of spectra.
The main advantage of this method is the possibility to get the estimation of
gamma velocity even from one spectroscopic observation with uncertain pulsation
phase. A detailed investigation of the LSD profile asymmetry shows that the
projection factor varies as a function of the pulsation phase -- this is a
key parameter which converts observed spectral line radial velocity variations
into photospheric pulsation velocities. As a byproduct of our study, we present
41 densely-spaced synthetic grids of LSD profile bisectors that are based on
atmospheric models of RR Lyr covering all pulsation phases.Comment: 17 pages, 16 figures, accepted for publication in MNRAS;
doi:10.1093/mnras/stx294
Identification of red supergiants in nearby galaxies with mid-IR photometry
The role of episodic mass loss in massive star evolution is one of the most
important open questions of current stellar evolution theory. Episodic mass
loss produces dust and therefore causes evolved massive stars to be very
luminous in the mid-infrared and dim at optical wavelengths. We aim to increase
the number of investigated luminous mid-IR sources to shed light on the late
stages of these objects. To achieve this we employed mid-IR selection criteria
to identity dusty evolved massive stars in two nearby galaxies. The method is
based on mid-IR colors, using 3.6 {\mu}m and 4.5 {\mu}m photometry from
archival Spitzer Space Telescope images of nearby galaxies and J-band
photometry from 2MASS. We applied our criteria to two nearby star-forming dwarf
irregular galaxies, Sextans A and IC 1613, selecting eight targets, which we
followed up with spectroscopy. Our spectral classification and analysis yielded
the discovery of two M-type supergiants in IC 1613, three K-type supergiants
and one candidate F-type giant in Sextans A, and two foreground M giants. We
show that the proposed criteria provide an independent way for identifying
dusty evolved massive stars, that can be extended to all nearby galaxies with
available Spitzer/IRAC images at 3.6 {\mu}m and 4.5 {\mu}m.Comment: 8 pages, 4 figures, A&A in pres
Chemical abundances of solar neighborhood RR Lyrae stars
We have analysed a sample of 18 RR Lyrae stars (17 fundamental-mode - RRab -
and one first overtone - RRc) and three Population II Cepheids (two BL Her
stars and one W Vir star), for which high-resolution (R 30000), high
signal-to-noise (S/N30) spectra were obtained with either SARG at the
Telescopio Nazionale Galileo (La Palma, Spain) or UVES at the ESO Very Large
Telescope (Paranal, Chile). Archival data were also analyzed for a few stars,
sampling 3 phases for each star. We obtained atmospheric parameters
(T, log, v, and [M/H]) and abundances of several
iron-peak and -elements (Fe, Cr, Ni, Mg, Ca, Si, and Ti) for different
pulsational phases, obtaining =+0.310.19 dex over the
entire sample covering -2.2[Fe/H]-1.1 dex. We find that silicon is indeed
extremely sensitive to the phase, as reported by previous authors, and cannot
be reliably determined. Apart from this, metallicities and abundance ratios are
consistently determined, regardless of the phase, within 0.10-0.15 dex,
although caution should be used in the range . Our
results agree with literature determinations for both variable and non-variable
field stars, obtained with very different methods, including low and
high-resolution spectroscopy. W Vir and BL Her stars, at least in the sampled
phases, appear indistinguishable from RRab from the spectroscopic analysis
point of view. Our large sample, covering all pulsation phases, confirms that
chemical abundances can be obtained for RR Lyrae with the classical EW-based
technique and static model atmospheres, even rather close to the shock phases.Comment: 16 pages, 8 figures, 7 tables (of which 1 electronic), accepted for
publication on MNRA
Properties of luminous red supergiant stars in the Magellanic Clouds
There is evidence that some red supergiants (RSGs) experience short lived
phases of extreme mass loss, producing copious amounts of dust. These episodic
outburst phases help to strip the hydrogen envelope of evolved massive stars,
drastically affecting their evolution. However, to date, the observational data
of episodic mass loss is limited. This paper aims to derive surface properties
of a spectroscopic sample of fourteen dusty sources in the Magellanic Clouds
using the Baade telescope. These properties may be used for future spectral
energy distribution fitting studies to measure the mass loss rates from present
circumstellar dust expelled from the star through outbursts. We apply MARCS
models to obtain the effective temperature () and extinction
() from the optical TiO bands. We use a routine to determine the
best fit model to the obtained spectra. We compute the using
empirical photometric relations and compare this to our modelled .
We have identified a new yellow supergiant and spectroscopically confirmed
eight new RSGs and one bright giant in the Magellanic Clouds. Additionally, we
observed a supergiant B[e] star and found that the spectral type has changed
compared to previous classifications, confirming that the spectral type is
variable over decades. For the RSGs, we obtained the surface and global
properties, as well as the extinction . Our method has picked up eight
new, luminous RSGs. Despite selecting dusty RSGs, we find values for that
are not as high as expected given the circumstellar extinction of these evolved
stars. The most remarkable object from the sample, LMC3, is an extremely
massive and luminous evolved massive star and may be grouped amongst the
largest and most luminous RSGs known in the Large Magellanic Cloud
(log(L/L5.5 and ).Comment: Accepted for publication in A&A. 17 pages, 14 figures, 4 table
Physical parameters of red supergiants in dwarf irregular galaxies in the Local Group
Increasing the statistics of evolved massive stars in the Local Group enables
investigating their evolution at different metallicities. During the late
stages of stellar evolution, the physics of some phenomena, such as episodic
and systematic mass loss, are not well constrained. For example, the physical
properties of red supergiants (RSGs) in different metallicity regimes remain
poorly understood. Thus, we initiated a systematic study of RSGs in dwarf
irregular galaxies (dIrrs) in the Local Group. The target selection is based on
3.6 m and 4.5 m photometry from archival Spitzer Space Telescope
images of nearby galaxies. We selected 46 targets in the dIrrs IC 10, IC 1613,
Sextans B, and the Wolf-Lundmark-Melotte (WLM) galaxy that we observed with the
GTC-OSIRIS and VLT-FORS2 instruments. We used several photometric techniques
together with a spectral energy distribution analysis to derive the
luminosities and effective temperatures of known and newly discovered RSGs. We
identified and spectroscopically confirmed 4 new RSGs, 5 previously known RSGs,
and 5 massive asymptotic giant branch (AGB) stars. We added known objects from
previous observations. In total, we present spectral classification and
fundamental physical parameters of 25 late-type massive stars in the following
dIrrs: Sextans A, Sextans B, IC 10, IC 1613, Pegasus, Phoenix, and WLM. This
includes 17 RSGs and 8 AGB stars that have been identified here and previously.
Based on our observational results and PARSEC evolutionary models, we draw the
following conclusions: (i) a trend to higher minimum effective temperatures at
lower metallicities and (ii) the maximum luminosity of RSGs appears to be
constant at () , independent of the
metallicity of the host environment (up to
dex).Comment: 22 pages, 17 figures, in press (A&A
Full orbital solution for the binary system in the northern Galactic disc microlensing event Gaia16aye
Gaia16aye was a binary microlensing event discovered in the direction towards the northern Galactic disc and was one of the first microlensing events detected and alerted to by the Gaia space mission. Its light curve exhibited five distinct brightening episodes, reaching up to I? =? 12 mag, and it was covered in great detail with almost 25 000 data points gathered by a network of telescopes. We present the photometric and spectroscopic follow-up covering 500 days of the event evolution. We employed a full Keplerian binary orbit microlensing model combined with the motion of Earth and Gaia around the Sun to reproduce the complex light curve. The photometric data allowed us to solve the microlensing event entirely and to derive the complete and unique set of orbital parameters of the binary lensing system. We also report on the detection of the first-ever microlensing space-parallax between the Earth and Gaia located at L2. The properties of the binary system were derived from microlensing parameters, and we found that the system is composed of two main-sequence stars with masses 0.57 ± 0.05 M? and 0.36 ± 0.03 M? at 780 pc, with an orbital period of 2.88 years and an eccentricity of 0.30. We also predict the astrometric microlensing signal for this binary lens as it will be seen by Gaia as well as the radial velocity curve for the binary system. Events such as Gaia16aye indicate the potential for the microlensing method of probing the mass function of dark objects, including black holes, in directions other than that of the Galactic bulge. This case also emphasises the importance of long-term time-domain coordinated observations that can be made with a network of heterogeneous telescopes
The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation
WEAVE, the new wide-field, massively multiplexed spectroscopic survey
facility for the William Herschel Telescope, will see first light in late 2022.
WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a
nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini'
integral field units (IFUs), and a single large IFU. These fibre systems feed a
dual-beam spectrograph covering the wavelength range 366959\,nm at
, or two shorter ranges at . After summarising the
design and implementation of WEAVE and its data systems, we present the
organisation, science drivers and design of a five- to seven-year programme of
eight individual surveys to: (i) study our Galaxy's origins by completing
Gaia's phase-space information, providing metallicities to its limiting
magnitude for 3 million stars and detailed abundances for
million brighter field and open-cluster stars; (ii) survey million
Galactic-plane OBA stars, young stellar objects and nearby gas to understand
the evolution of young stars and their environments; (iii) perform an extensive
spectral survey of white dwarfs; (iv) survey
neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and
kinematics of stellar populations and ionised gas in cluster galaxies;
(vi) survey stellar populations and kinematics in field galaxies
at ; (vii) study the cosmic evolution of accretion
and star formation using million spectra of LOFAR-selected radio sources;
(viii) trace structures using intergalactic/circumgalactic gas at .
Finally, we describe the WEAVE Operational Rehearsals using the WEAVE
Simulator.Comment: 41 pages, 27 figures, accepted for publication by MNRA
The wide-field, multiplexed, spectroscopic facility WEAVE : survey design, overview, and simulated implementation
Funding for the WEAVE facility has been provided by UKRI STFC, the University of Oxford, NOVA, NWO, Instituto de Astrofísica de Canarias (IAC), the Isaac Newton Group partners (STFC, NWO, and Spain, led by the IAC), INAF, CNRS-INSU, the Observatoire de Paris, Région Île-de-France, CONCYT through INAOE, Konkoly Observatory (CSFK), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Lund University, the Leibniz Institute for Astrophysics Potsdam (AIP), the Swedish Research Council, the European Commission, and the University of Pennsylvania.WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366-959 nm at R ∼ 5000, or two shorter ranges at R ∼ 20,000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for ∼ 3 million stars and detailed abundances for ∼ 1.5 million brighter field and open-cluster stars; (ii) survey ∼ 0.4 million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey ∼ 400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in z 1 million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at z > 2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator.PostprintPeer reviewe
The wide-field, multiplexed, spectroscopic facility WEAVE: Survey design, overview, and simulated implementation
WEAVE, the new wide-field, massively multiplexed spectroscopic survey facility for the William Herschel Telescope, will see first light in late 2022. WEAVE comprises a new 2-degree field-of-view prime-focus corrector system, a nearly 1000-multiplex fibre positioner, 20 individually deployable 'mini' integral field units (IFUs), and a single large IFU. These fibre systems feed a dual-beam spectrograph covering the wavelength range 366−959\,nm at R∼5000, or two shorter ranges at R∼20000. After summarising the design and implementation of WEAVE and its data systems, we present the organisation, science drivers and design of a five- to seven-year programme of eight individual surveys to: (i) study our Galaxy's origins by completing Gaia's phase-space information, providing metallicities to its limiting magnitude for ∼3 million stars and detailed abundances for ∼1.5 million brighter field and open-cluster stars; (ii) survey ∼0.4 million Galactic-plane OBA stars, young stellar objects and nearby gas to understand the evolution of young stars and their environments; (iii) perform an extensive spectral survey of white dwarfs; (iv) survey ∼400 neutral-hydrogen-selected galaxies with the IFUs; (v) study properties and kinematics of stellar populations and ionised gas in z1 million spectra of LOFAR-selected radio sources; (viii) trace structures using intergalactic/circumgalactic gas at z>2. Finally, we describe the WEAVE Operational Rehearsals using the WEAVE Simulator
Chemical composition of semi-regular variable giants. II.
Aims. The aim of this work was to derive the elemental abundances in four stars
classified as semiregular variables of the type “d” (SRd). These stars should presumably
belong to the Galactic halo population.
Methods. Elemental abundances have been derived from both local thermodynamical equilibrium (LTE) and
non-local thermodynamical equilibrium (NLTE) analyses, applied to high-resolution (R ≅ 80 000)
spectra obtained with the CFHT ESPaDOnS spectrograph.
Results. We have derived the abundances of 29 chemical elements in V463 Her, V894 Her,
CW CVn, and MS Hya, and arrived at the following conclusions.
Conclusions. The stars of our programme have a chemical composition that does not agree with their presumable status
as metal-deficient halo giants. All studied SRd giants have relative-to-solar elemental abundances typical
of the thick/thin Galactic disc stars