66 research outputs found
Distance and age of the massive stellar cluster Westerlund 1. I. Parallax method using Gaia-EDR3
Westerlund 1 (Wd 1) is one of the most massive young star clusters in the
Milky Way. Although relevant for star formation and evolution, its fundamental
parameters are not yet very well constrained. Our goal is to derive an accurate
distance and provide constraints on the cluster age. We used the photometric
and astrometric information available in the Gaia Early Data Release 3
(Gaia-EDR3) to infer its distance of 4.06 kpc. Modelling of
the eclipsing binary system W36 reported in Paper II led to the distance of
4.340.25 kpc, in agreement with the Gaia-EDR3 distance and, therefore,
validating the parallax zero-point correction approach appropriate for red
objects. By taking advantage of another two recent distance determinations
using the Gaia-EDR3, we obtained a weighted mean distance for the cluster as
d=4.23 kpc (=13.13 mag),
which has an unprecedented accuracy of 4\%. We adopted recent Geneva
evolutionary tracks for supra-solar metallicity objects to infer the age of the
faintest RSG source from Wd 1, leading to a cluster age of 11.00.5 Myr, in
excellent agreement with recent work by Beasor \& Davies (10.4
Myr) based on MIST evolutionary models. The age of W36 was reported to be
3.50.5 Myr in Paper II, supporting recent claims of a temporal spread of
several Myr for the star-forming process within Wd 1 instead of a monolithic
starburst scenario.Comment: 16 pages, 9 figures, revised version submitted to MNRAS on April
20th, 202
He II 4686 emission from the massive binary system in Car: constraints to the orbital elements and the nature of the periodic minima
{\eta} Carinae is an extremely massive binary system in which rapid spectrum
variations occur near periastron. Most notably, near periastron the He II
line increases rapidly in strength, drops to a minimum value,
then increases briefly before fading away. To understand this behavior, we
conducted an intense spectroscopic monitoring of the He II
emission line across the 2014.6 periastron passage using ground- and
space-based telescopes. Comparison with previous data confirmed the overall
repeatability of EW(He II ), the line radial velocities, and the
timing of the minimum, though the strongest peak was systematically larger in
2014 than in 2009 by 26%. The EW(He II ) variations, combined
with other measurements, yield an orbital period d. The observed
variability of the EW(He II ) was reproduced by a model in which
the line flux primarily arises at the apex of the wind-wind collision and
scales inversely with the square of the stellar separation, if we account for
the excess emission as the companion star plunges into the hot inner layers of
the primary's atmosphere, and including absorption from the disturbed primary
wind between the source and the observer. This model constrains the orbital
inclination to -, and the longitude of periastron to
-. It also suggests that periastron passage occurred on
d. Our model also reproduced EW(He II )
variations from a polar view of the primary star as determined from the
observed He II emission scattered off the Homunculus nebula.Comment: The article contains 23 pages and 17 figures. It has been accepted
for publication in Ap
Eta Carinae: an evolving view of the central binary, its interacting winds and its foreground ejecta
FUV spectra of Eta Car, recorded across two decades with HST/STIS, document
multiple changes in resonant lines caused by dissipating extinction in our line
of sight. The FUV flux has increased nearly ten-fold which has led to increased
ionization of the multiple shells within the Homunculus and photo-destruction
of molecular hydrogen. Comparison of observed resonant line profiles with
CMFGEN model profiles allows separation of wind-wind collision and shell
absorptions from the primary wind, P Cygni profiles.The dissipating occulter
preferentially obscured the central binary and interacting winds relative to
the very extended primary wind. We are now able to monitor changes in the
colliding winds with orbital phase. High velocity transient absorptions
occurred across the most recent periastron passage, indicating acceleration of
the primary wind by the secondary wind which leads to a downstream, high
velocity bowshock that is newly generated every orbital period. There is no
evidence of changes in the properties of the binary winds.Comment: 36 pages, 22 figures, accepted Astrophysical Journa
Distinguishing circumstellar from stellar photometric variability in Eta Carinae
The interacting binary Eta Carinae remains one of the most enigmatic massive stars in our Galaxy despite over four centuries of observations. In this work, its light curve from the ultraviolet to the near-infrared is analysed using spatially resolved HST observations and intense monitoring at the La Plata Observatory, combined with previously published photometry. We have developed a method to separate the central stellar object in the ground-based images using HST photometry and applying it to the more numerous ground-based data, which supports the hypothesis that the central source is brightening faster than the almost-constant Homunculus. After detrending from long-term brightening, the light curve shows periodic orbital modulation (V ⌠0.6 mag) attributed to the windâwind collision cavity as it sweeps around the primary star and it shows variable projected area to our line-of-sight. Two quasi-periodic components with time-scales of 2â3 and 8â10 yr and low amplitude, V < 0.2 mag, are superimposed on the brightening light curve, being the only stellar component of variability found, which indicates minimal stellar instability. Moreover, the light-curve analysis shows no evidence of âshell ejectionsâ at periastron. We propose that the long-term brightening of the stellar core is due to the dissipation of a dusty clump in front of the central star, which works like a natural coronagraph. Thus, the central stars appear to be more stable than previously thought since the dominant variability originates from a changing circumstellar medium. We predict that the brightening phase, due mainly to dust dissipation, will be completed around 2032 ± 4 yr, when the star will be brighter than in the 1600s by up to V ⌠1 mag.Fil: Damineli, A.. Universidade do Sao Paulo. Instituto de Astronomia, GeofĂsica e CiĂȘncias AtmosfĂ©ricas; BrasilFil: Fernandez Lajus, Eduardo Eusebio. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: Almeida, L.A.. Universidade do Sao Paulo. Instituto de Astronomia, GeofĂsica e CiĂȘncias AtmosfĂ©ricas; Brasil. Universidade Federal do Rio Grande do Norte; BrasilFil: Corcoran, M.F.. National Aeronautics and Space Administration; Estados Unidos. The Catholic University of America; Estados UnidosFil: Damineli, D.S.C.. University of Maryland; Estados UnidosFil: Gull, T.R.. National Aeronautics and Space Administration; Estados UnidosFil: Hamaguchi, K. National Aeronautics and Space Administration; Estados Unidos. University of Maryland; Estados UnidosFil: Hillier, D.J.. University of Pittsburgh; Estados UnidosFil: Jablonski, F.J.. Centro de Previsao de Tempo e Estudos ClimĂĄticos. Instituto Nacional de Pesquisas Espaciais; BrasilFil: Madura, T.I.. San Jose State University; Estados UnidosFil: Moffat, A.F.J.. UniversitĂ© du QuĂ©bec a Montreal; CanadĂĄFil: Navarete, F.. Universidade do Sao Paulo. Instituto de Astronomia, GeofĂsica e CiĂȘncias AtmosfĂ©ricas; BrasilFil: Richardson, N.D.. University Of Toledo (utoledo); Estados UnidosFil: Ruiz, G.F.. Universidade do Sao Paulo. Instituto de Astronomia, GeofĂsica e CiĂȘncias AtmosfĂ©ricas; BrasilFil: Salerno, N.E.. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; ArgentinaFil: Scalia, MarĂa Cecilia. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Instituto de AstrofĂsica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas. Instituto de AstrofĂsica La Plata; ArgentinaFil: Weigelt, G.. Max Planck Institute For Radio Astronomy; Alemani
He II λ4686 emission from the massive binary system in η car: constraints to the orbital elements and the nature of the periodic minima
Eta Carinae (η Car) is an extremely massive binary system in which rapid spectrum variations occur near periastron. Most notably, near periastron the He ii λ4686 line increases rapidly in strength, drops to a minimum value, then increases briefly before fading away. To understand this behavior, we conducted an intense spectroscopic monitoring of the He ii λ4686 emission line across the 2014.6 periastron passage using ground- and space-based telescopes. Comparison with previous data confirmed the overall repeatability of the line equivalent width (EW), radial velocities, and the timing of the minimum, though the strongest peak was systematically larger in 2014 than in 2009 by 26%. The EW variations, combined with other measurements, yield an orbital period of 2022.7 ±0.3 days. The observed variability of the EW was reproduced by a model in which the line flux primarily arises at the apex of the wind-wind collision and scales inversely with the square of the stellar separation, if we account for the excess emission as the companion star plunges into the hot inner layers of the primary's atmosphere, and including absorption from the disturbed primary wind between the source and the observer. This model constrains the orbital inclination to 135°-153°, and the longitude of periastron to 234°-252°. It also suggests that periastron passage occurred on days). Our model also reproduced EW variations from a polar view of the primary star as determined from the observed He ii λ4686 emission scattered off the Homunculus nebula.Facultad de Ciencias AstronĂłmicas y GeofĂsica
The apparent eta Carinae's long-term evolution and the critical role played by the strengthening of P Cygni absorption lines
Over the entire 20th century, Eta Carinae (\ec) has displayed a unique
spectrum, which recently has been evolving towards that of a typical LBV. The
two competing scenarios to explain such evolution are: (1) a dissipating
occulter in front of a stable star or (2) a decreasing mass loss rate of the
star. The first mechanism simultaneously explains why the central star appears
to be secularly increasing its apparent brightness while its luminosity does
not change; why the Homunculus' apparent brightness remains almost constant;
and why the spectrum seen in direct light is becoming more similar to that
reflected from the Homunculus (and which resembles a typical LBV). The second
scenario does not account for these facts and predicts an increase in the
terminal speed of the wind, contrary to observations. In this work, we present
new data showing that the P Cygni absorption lines are secularly strengthening,
which is not the expected behaviour for a decreasing wind-density scenario.
CMFGEN modelling of the primary's wind with a small occulter in front agrees
with observations. One could argue that invoking a dissipating coronagraphic
occulter makes this object even more peculiar than it already appears to be.
However, on the contrary, it solves the apparent contradictions between many
observations. Moreover, by assigning the long-term behaviour to circumstellar
causes and the periodic variations due to binarity, a star more stable after
the 1900s than previously thought is revealed, contrary to the earlier paradigm
of an unpredictable object.Comment: 17 pages, 12 figures, submitted to MNRA
The Stellar Content of Obscured Galactic Giant HII Regions. VII. W3
Spectrophotometric distances in the K band have been reported by different
authors for a number of obscured Galactic HII regions. Almost 50% of them show
large discrepancies compared to the classical method using radial velocities
measured in the radio spectral region. In order to provide a crucial test of
both methods, we selected a target which does not present particular difficulty
for any method and which has been measured by as many techniques as possible.
The W3 star forming complex, located in the Perseus arm, offers a splendid
opportunity for such a task. We used the NIFS spectrograph on the Frederick C.
Gillett Gemini North telescope to classify candidate "naked photosphere" OB
stars based on 2MASS photometry. Two of the targets are revealed to be mid
O-type main sequence stars leading to a distance of d = 2.20 kpc. This is in
excellent agreement with the spectrophotometric distance derived in the optical
band (d = 2.18 kpc, Humphreys 1978) and with a measurement of the W3
trigonometric parallax (d = 1.95 kpc, Xu et al. 2006). Such results confirm
that the spectrophotometric distances in the K band are reliable. The radio
derived kinematic distance, on the contrary, gives a distance twice as large (d
= 4.2 kpc, Russeil 2003). This indicates that this region of Perseus arm does
not follow the Galactic rotation curve, and this may be the case also for other
HII regions for which discrepancies have been found
He II λ4686 emission from the massive binary system in η car: constraints to the orbital elements and the nature of the periodic minima
Eta Carinae (η Car) is an extremely massive binary system in which rapid spectrum variations occur near periastron. Most notably, near periastron the He ii λ4686 line increases rapidly in strength, drops to a minimum value, then increases briefly before fading away. To understand this behavior, we conducted an intense spectroscopic monitoring of the He ii λ4686 emission line across the 2014.6 periastron passage using ground- and space-based telescopes. Comparison with previous data confirmed the overall repeatability of the line equivalent width (EW), radial velocities, and the timing of the minimum, though the strongest peak was systematically larger in 2014 than in 2009 by 26%. The EW variations, combined with other measurements, yield an orbital period of 2022.7 ±0.3 days. The observed variability of the EW was reproduced by a model in which the line flux primarily arises at the apex of the wind-wind collision and scales inversely with the square of the stellar separation, if we account for the excess emission as the companion star plunges into the hot inner layers of the primary's atmosphere, and including absorption from the disturbed primary wind between the source and the observer. This model constrains the orbital inclination to 135°-153°, and the longitude of periastron to 234°-252°. It also suggests that periastron passage occurred on days). Our model also reproduced EW variations from a polar view of the primary star as determined from the observed He ii λ4686 emission scattered off the Homunculus nebula.Facultad de Ciencias AstronĂłmicas y GeofĂsica
Herschelobservations of the W3 GMC (II): clues to the formation of clusters of high-mass stars
The W3 giant molecular cloud is a prime target for investigating the formation of high-mass stars and clusters. This second study of W3 within the HOBYS Key Program provides a comparative analysis of subfields within W3 to further constrain the processes leading to the observed structures and stellar population. Probability density
functions (PDFs) and cumulative mass distributions (CMDs) were created from dust column density maps, quantified as extinction AV. The shape of the PDF, typically represented with a lognormal function at low Av âbreakingâ to a power-law tail at high Av, is influenced by various processes including turbulence and selfgravity. The breaks can also be identified, often more readily, in the CMDs. The PDF break from lognormal (Av(SF)» 6â10 mag) appears to shift to higher Av by stellar feedback, so that high-mass star-forming regions tend to have higher PDF breaks. A second break at Av> 50 mag traces structures formed or influenced by a dynamic process. Because such a process has been suggested to drive high-mass star formation in W3, this second
break might then identify regions with potential for hosting high-mass stars/clusters. Stellar feedback appears to be a major mechanism driving the local evolution and state of regions within W3. A high initial star formation efficiency in a dense medium could result in a self-enhancing process, leading to more compression and favorable
star formation conditions (e.g., colliding flows), a richer stellar content, and massive stars. This scenario would be compatible with the âconvergent constructive feedbackâ model introduced in our previous Herschel study
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