28 research outputs found
Extragalactic Star-forming Regions: a Study of the Physical Properties and Chemical Abundances
Extragalactic star-forming regions are characterized by the large number of young and massive stars that ionize the surrounding gas. These regions can be observed as very luminous spots in the disk of spiral galaxies and as large areas in Blue Compact Dwarf galaxies. We present preliminary results of the study of a sample of star-forming regions in two spiral and one Blue Compact Dwarf galaxies observed with the GMOS/Long-slit configuration on the Gemini-South Telescope. We are presenting a preliminary study of two regions of each galaxy for which we estimated: reddening, electron densities, and electron temperatures by using direct method, temperature relations based on photoionization models, and empirical relations. From the electron temperatures we de- rived ionic and total chemical abundances of, O, S, N, Ne, Ar and He. In addition we computed star formation rates and the ionization state for all regions.Fil: Muñoz Vergara, D.. Gemini Observatory; Chile. Universidad de La Serena; ChileFil: Firpo, V.. Gemini Observatory; Chile. Universidad de La Serena; ChileFil: HĂ€gele, Guillermo Federico. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. 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: Bosch, Guillermo Luis. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. 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: Cardaci, Monica Viviana. Universidad Nacional de La Plata. Facultad de Ciencias AstronĂłmicas y GeofĂsicas; Argentina. 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: Sanmartim, D.. Gemini Observatory; ChileFil: Gimeno, G.. Gemini Observatory; ChileII workshop on Chemical Abundances in Gaseous Nebulae: Open problems in Nebular AstrophysicsSao Jose dos CamposBrasilUniversidade do Vale do ParaĂb
A study of the neglected Galactic HII region NGC 2579 and its companion ESO 370-9
The Galactic HII region NGC 2579 has stayed undeservedly unexplored due to
identification problems which persisted until recently. Both NGC 2579 and its
companion ESO 370-9 have been misclassified as planetary or reflection nebula,
confused with each other and with other objects. Due to its high surface
brightness, high excitation, angular size of few arcminutes and relatively low
interstellar extinction, NGC 2579 is an ideal object for investigations in the
optical range. Located in the outer Galaxy, NGC 2579 is an excellent object for
studying the Galactic chemical abundance gradients. In this paper we present
the first comprehensive observational study on the nebular and stellar
properties of NGC 2579 and ESO 370-9, including the determination of electron
temperature, density structure, chemical composition, kinematics, distance, and
the identification and spectral classification of the ionizing stars, and
discuss the nature of ESO 370-9. Long slit spectrophotometric data in the
optical range were used to derive the nebular electron temperature, density and
chemical abundances and for the spectral classification of the ionizing star
candidates. Halpha and UBV CCD photometry was carried out to derive stellar
distances from spectroscopic parallax and to measure the ionizing photon flux.Comment: To be published in Astronomy & Astrophysic
The VISCACHA survey -- VIII. Chemical evolution history of Small Magellanic Cloud West Halo cluster
The chemical evolution history of the Small Magellanic Cloud (SMC) has been a
matter of debate for decades. The challenges in understanding the SMC chemical
evolution are related to a very slow star formation rate (SFR) combined with
bursts triggered by the multiple interactions between the SMC and the Large
Magellanic Cloud, a significant (~0.5 dex) metallicity dispersion for the SMC
cluster population younger than about 7.5 Gyr, and multiple chemical evolution
models tracing very different paths through the observed age-metallicity
relation of the SMC. There is no doubt that these processes were complex.
Therefore, a step-by-step strategy is required in order to better understand
the SMC chemical evolution. We adopted an existing framework to split the SMC
into regions on the sky, and we focus on the west halo in this work, which
contains the oldest and most metal-poor stellar populations and is moving away
from the SMC, that is, in an opposite motion with respect to the Magellanic
Bridge. We present a sample containing ~60% of all west halo clusters to
represent the region well, and we identify a clear age-metallicity relation
with a tight dispersion that exhibits a 0.5 dex metallicity dip about 6 Gyr
ago. We ran chemical evolution models and discuss possible scenarios to explain
this metallicity dip, the most likely being a major merger accelerating the SFR
after the event. This merger should be combined with inefficient internal gas
mixing within the SMC and different SFRs in different SMC regions because the
same metallicity dip is not seen in the AMR of the SMC combining clusters from
all regions. We try to explain the scenario to better understand the SMC
chemo-dynamical history.Comment: 16 pages, 8 figures, 3 tables, Accepted for publication in Astronomy
& Astrophysics journal
The VISCACHA survey -- VII. Assembly history of the Magellanic Bridge and SMC Wing from star clusters
The formation scenario of the Magellanic Bridge during an encounter between
the Large and Small Magellanic Clouds Myr ago, as proposed by
-body models, would be imprinted in the chemical enrichment and kinematics
of its stars, and sites of ongoing star formation along its extension. We
present an analysis of 33 Bridge star clusters using photometry obtained with
the SOAR 4-m telescope equipped with adaptive optics for the VISCACHA survey.
We performed a membership selection and derived self-consistent ages,
metallicities, distances and reddening values via statistical isochrone
fitting, as well as tidal radii and integrated masses from structure analysis.
Two groups are clearly detected: 13 well-studied clusters older than the
Bridge, with Gyr and dex; and 15 clusters with
dex, probably formed in-situ. The old
clusters follow the overall age and metallicity gradients of the SMC, whereas
the younger ones are uniformly distributed along the Bridge. The main results
are as follows: we derive ages and metallicities for the first time for 9
and 18 clusters, respectively; we detect two metallicity dips in the
age-metallicity relation of the Bridge at Myr and Gyr ago
for the first time, possibly chemical signatures of the formation of the Bridge
and Magellanic Stream; we estimate a minimum stellar mass for the
Bridge of ; we confirm that all the young
Bridge clusters at are metal-rich dex.Comment: 15 pages, 13 figures + appendix. Accepted for publication in MNRA
AGN STORM 2: V. Anomalous Behavior of the CIV Light Curve in Mrk 817
An intensive reverberation mapping campaign on the Seyfert 1 galaxy Mrk817
using the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST)
revealed significant variations in the response of the broad UV emission lines
to fluctuations in the continuum emission. The response of the prominent UV
emission lines changes over a 60-day duration, resulting in distinctly
different time lags in the various segments of the light curve over the 14
months observing campaign. One-dimensional echo-mapping models fit these
variations if a slowly varying background is included for each emission line.
These variations are more evident in the CIV light curve, which is the line
least affected by intrinsic absorption in Mrk817 and least blended with
neighboring emission lines. We identify five temporal windows with distinct
emission line response, and measure their corresponding time delays, which
range from 2 to 13 days. These temporal windows are plausibly linked to changes
in the UV and X-ray obscuration occurring during these same intervals. The
shortest time lags occur during periods with diminishing obscuration, whereas
the longest lags occur during periods with rising obscuration. We propose that
the obscuring outflow shields the ultraviolet broad lines from the ionizing
continuum. The resulting change in the spectral energy distribution of the
ionizing continuum, as seen by clouds at a range of distances from the nucleus,
is responsible for the changes in the line response.Comment: 20 pages, 8 figures, submitted to Ap
AGN STORM 2. IV. Swift X-ray and ultraviolet/optical monitoring of Mrk 817
The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping
project designed to trace out the structure of Mrk 817 from the inner accretion
disk to the broad emission line region and out to the dusty torus. As part of
this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15
months, obtaining observations in X-rays and six UV/optical filters. The X-ray
monitoring shows that Mrk 817 was in a significantly fainter state than in
previous observations, with only a brief flare where it reached prior flux
levels. The X-ray spectrum is heavily obscured. The UV/optical light curves
show significant variability throughout the campaign and are well correlated
with one another, but uncorrelated with the X-rays. Combining the Swift
UV/optical light curves with Hubble UV continuum light curves, we measure
interband continuum lags, , that increase with increasing
wavelength roughly following , the
dependence expected for a geometrically thin, optically thick, centrally
illuminated disk. Modeling of the light curves reveals a period at the
beginning of the campaign where the response of the continuum is suppressed
compared to later in the light curve - the light curves are not simple shifted
and scaled versions of each other. The interval of suppressed response
corresponds to a period of high UV line and X-ray absorption, and reduced
emission line variability amplitudes. We suggest that this indicates a
significant contribution to the continuum from the broad line region gas that
sees an absorbed ionizing continuum.Comment: 20 pages, 13 figures, 3 tables, accepted for publication in Ap
AGN STORM 2. IV. Swift X-Ray and Ultraviolet/Optical Monitoring of Mrk 817
The AGN STORM 2 campaign is a large, multiwavelength reverberation mapping project designed to trace out the structure of Mrk 817 from the inner accretion disk to the broad emission line region and out to the dusty torus. As part of this campaign, Swift performed daily monitoring of Mrk 817 for approximately 15 months, obtaining observations in X-rays and six UV/optical filters. The X-ray monitoring shows that Mrk 817 was in a significantly fainter state than in previous observations, with only a brief flare where it reached prior flux levels. The X-ray spectrum is heavily obscured. The UV/optical light curves show significant variability throughout the campaign and are well correlated with one another, but uncorrelated with the X-rays. Combining the Swift UV/optical light curves with Hubble Space Telescope UV continuum light curves, we measure interband continuum lags, Ï(λ), that increase with increasing wavelength roughly following Ï(λ) â λ 4/3, the dependence expected for a geometrically thin, optically thick, centrally illuminated disk. Modeling of the light curves reveals a period at the beginning of the campaign where the response of the continuum is suppressed compared to later in the light curveâthe light curves are not simple shifted and scaled versions of each other. The interval of suppressed response corresponds to a period of high UV line and X-ray absorption, and reduced emission line variability amplitudes. We suggest that this indicates a significant contribution to the continuum from the broad-line region gas that sees an absorbed ionizing continuum
AGN STORM 2. VI. Mapping Temperature Fluctuations in the Accretion Disk of Mrk 817
We fit the UV/optical lightcurves of the Seyfert 1 galaxy Mrk 817 to produce maps of the accretion disk temperature fluctuations ÎŽ T resolved in time and radius. The ÎŽ T maps are dominated by coherent radial structures that move slowly (v âȘ c) inward and outward, which conflicts with the idea that disk variability is driven only by reverberation. Instead, these slow-moving temperature fluctuations are likely due to variability intrinsic to the disk. We test how modifying the input lightcurves by smoothing and subtracting them changes the resulting ÎŽ T maps and find that most of the temperature fluctuations exist over relatively long timescales (hundreds of days). We show how detrending active galactic nucleus (AGN) lightcurves can be used to separate the flux variations driven by the slow-moving temperature fluctuations from those driven by reverberation. We also simulate contamination of the continuum emission from the disk by continuum emission from the broad-line region (BLR), which is expected to have spectral features localized in wavelength, such as the Balmer break contaminating the U band. We find that a disk with a smooth temperature profile cannot produce a signal localized in wavelength and that any BLR contamination should appear as residuals in our model lightcurves. Given the observed residuals, we estimate that only âŒ20% of the variable flux in the U and u lightcurves can be due to BLR contamination. Finally, we discus how these maps not only describe the data but can make predictions about other aspects of AGN variability
Sapaki: Galactic O3If* star possibly born in isolation
Context. The study of high-mass stars found to be isolated in the field of the Milky Way may help to probe the feasibility of the core-accretion mechanism in the case of massive star formation. The existence of truly isolated stars may efficiently probe the possibility that individual massive stars can be born in isolation.
Aims. We observed WR67a (hereafter Sapaki), an O3If* star that appears to be isolated close to the center of a well-developed giant cavity that is aptly traced by 8.0 ÎŒm hot dust emission.
Methods. We acquired medium-resolution (Rââ=ââ4100) and moderate signal-to-noise (S/Nââ=ââ95 at 4500 Ă
) spectra for Sapaki in the range of 3800â
ââ
10â500 Ă
with the Magellan Echellette (MagE) at Las Campanas Observatory. We computed the line-of-sight total extinctions. Additionally, we restricted its heliocentric distance by using a range of different estimators. Moreover, we measured its radial velocity from several lines in its spectrum. Finally, we analyzed its proper motions from Gaia to examine its possible runaway status.
Results. The star has been classified as having the spectral type O3If* given its resemblance to standard examples of the class. In addition, we found that Sapaki is highly obscured, reaching a line-of-sight extinction value of AVâ=â7.87. We estimated the heliocentric distance to be in the range of dâ=â4â
ââ
7 kpc. We also estimated its radial velocity to be Vrâ=ââ34.2â
屉
15.6 km sâ1. We may also discard its runaway status solely based on its 2D kinematics. Furthermore, by analyzing proper motions and parallaxes provided by Gaia, we found only one other star with compatible measurements.
Conclusions. Given its apparent non-runaway status and the absence of clustering, Sapaki appears to be a solid candidate for isolated high-mass star formation in the Milky Way