Rodolfo Angeloni | Universidad de La Serena-Chile (original) (raw)

Papers by Rodolfo Angeloni

Proceedings of the International Astronomical Union, 2012

The VISTA Variables in the Vía Láctea (VVV) survey is one of six public ESO surveys, and is now i... more The VISTA Variables in the Vía Láctea (VVV) survey is one of six public ESO surveys, and is now in its 4th year of observing. Although far from being complete, the VVV survey has already delivered many results, some directly connected to the intended science goals (detection of variables stars, microlensing events, new star clusters), others concerning more exotic objects, e.g. novae. Now, at the end of the fourth observing period, and comprising roughly 50% of the proposed observations, the actual status of the survey, as well some of the results based on the VVV data, are presented.

Powered by a supermassive black hole with an accretion disk, the spectra of active galactic nucle... more Powered by a supermassive black hole with an accretion disk, the spectra of active galactic nuclei (AGNs) are characterized by prominent emission lines including Balmer lines. The unification schemes of AGNs require the existence of a thick molecular torus that may hide the broad emission line region from the view of observers near the equatorial direction. In this configuration, one may expect that the far UV radiation from the central engine can be Raman scattered by neutral hydrogen to reappear around Balmer and Paschen emission lines which can be identified with broad wings. We produce Hα, Hβ and Paα wings using a Monte Carlo technique to investigate their properties. The neutral scattering region is assumed to be a cylindrical torus specified by the inner and outer radii and the height. While the covering factor of the scattering region affects the overall strengths of the wings, the wing widths are primarily dependent on the neutral hydrogen column density NHI being roughly proportional to N1/2HI. In particular, with NHI=1023 cm−2 the Hα wings typically show a width ∼2×104 km s−1. We also find that Hα and Paα wing profiles are asymmetric with the red part stronger than the blue part and an opposite behavior is seen for Hβ wings.

We present the results of a spectroscopic follow-up of various puzzling variable objects detected... more We present the results of a spectroscopic follow-up of various puzzling variable objects detected in the OGLE-III Galactic disk and bulge fields. The sample includes mainly short-period multi-mode pulsating stars that could not have been unambiguously classified as either δ Sct or β Cep type stars based on photometric data only, also stars with irregular fluctuations mimicking cataclysmic variables and stars with dusty shells, and periodic variables displaying brightenings in their light curves that last for more than half of the period. The obtained low-resolution spectra show that all observed short-period pulsators are of δ Sct type, the stars with irregular fluctuations are young stellar objects, and the objects with regular brightenings are A type stars or very likely Ap stars with strong magnetic field responsible for the presence of bright caps around magnetic poles on their surface. We also took spectra of objects designated OGLE-GD-DSCT-0058 and OGLE-GD-CEP-0013. An estimated effective temperature of 33 000 K in OGLE-GD-DSCT-0058 indicates that it cannot be a δ Sct type variable. This very short-period (0.01962 d) high-amplitude (0.24 mag in the I-band) object remains a mystery. It may represent a new class of variable stars. The spectrum of OGLE-GD-CEP-0013 confirms that this is a classical Cepheid despite a peculiar shape of its light curve. The presented results will help in proper classification of variable objects in the OGLE Galaxy Variability Survey.

Context. Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitat... more Context. Stellar variability in the near-infrared (NIR) remains largely unexplored. The exploitation of public science archives with data-mining methods offers a perspective for a time-domain exploration of the NIR sky.
Aims: We perform a comprehensive search for stellar variability using the optical-NIR multiband photometric data in the public Calibration Database of the WFCAM Science Archive (WSA), with the aim of contributing to the general census of variable stars and of extending the current scarce inventory of accurate NIR light curves for a number of variable star classes.
Methods: Standard data-mining methods were applied to extract and fine-tune time-series data from the WSA. We introduced new variability indices designed for multiband data with correlated sampling, and applied them for preselecting variable star candidates, i.e., light curves that are dominated by correlated variations, from noise-dominated ones. Preselection criteria were established by robust numerical tests for evaluating the response of variability indices to the colored noise characteristic of the data. We performed a period search using the string-length minimization method on an initial catalog of 6551 variable star candidates preselected by variability indices. Further frequency analysis was performed on positive candidates using three additional methods in combination, in order to cope with aliasing.
Results: We find 275 periodic variable stars and an additional 44 objects with suspected variability with uncertain periods or apparently aperiodic variation. Only 44 of these objects had been previously known, including 11 RR Lyrae stars on the outskirts of the globular cluster M 3 (NGC 5272). We provide a preliminary classification of the new variable stars that have well-measured light curves, but the variability types of a large number of objects remain ambiguous. We classify most of the new variables as contact binary stars, but we also find several pulsating stars, among which 34 are probably new field RR Lyrae, and 3 are likely Cepheids. We also identify 32 highly reddened variable objects close to previously known dark nebulae, suggesting that these are embedded young stellar objects. We publish our results and all light curve data as the WFCAM Variable Star Catalog.
Tables 4-6 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/573/A100

BOMBOLO is a new multi-passband visitor instrument for the SOAR observatory. It is a three-arm im... more BOMBOLO is a new multi-passband visitor instrument for the SOAR observatory. It is a three-arm imager covering the near-UV and optical wavelengths. The three arms work simultaneously and independently, providing synchronized imaging capability for rapid astronomical events. BOMBOLO leading science cases are: 1) Simultaneous Multiband Flickering Studies of Accretion Phenomena; 2) Near UV/Optical Diagnostics of Stellar Evolutionary Phases; 3) Exoplanetary Transits; 4) Microlensing Follow-Up and 5) Solar Systems Studies. The instrument is at the Conceptual Design stage, having been approved by the SOAR Board of Directors as a visitor instrument in 2012 and having been granted full funding from CONICYT, the Chilean State Agency of Research, in 2013. The Design Phase has begun and will be completed in late 2014, followed by a construction phase in 2015 and 2016A, with expected Commissioning in 2016B and 2017A. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Context. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey is a variability survey of... more Context. The Vista Variables in the Vía Láctea (VVV) ESO Public Survey is a variability survey of the Milky Way bulge and an adjacent section of the disk carried out from 2010 on ESO Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey will eventually deliver a deep near-IR atlas with photometry and positions in five passbands (ZYJHKS) and a catalogue of 1-10 million variable point sources - mostly unknown - that require classifications.
Aims: The main goal of the VVV Templates Project, which we introduce in this work, is to develop and test the machine-learning algorithms for the automated classification of the VVV light-curves. As VVV is the first massive, multi-epoch survey of stellar variability in the near-IR, the template light-curves that are required for training the classification algorithms are not available. In the first paper of the series we describe the construction of this comprehensive database of infrared stellar variability.
Methods: First, we performed a systematic search in the literature and public data archives; second, we coordinated a worldwide observational campaign; and third, we exploited the VVV variability database itself on (optically) well-known stars to gather high-quality infrared light-curves of several hundreds of variable stars.
Results: We have now collected a significant (and still increasing) number of infrared template light-curves. This database will be used as a training-set for the machine-learning algorithms that will automatically classify the light-curves produced by VVV. The results of such an automated classification will be covered in forthcoming papers of the series.

Symbiotic stars are long-orbital-period interacting binaries characterized by extended emission o... more Symbiotic stars are long-orbital-period interacting binaries characterized by extended emission over the whole electromagnetic range and by complex photometric and spectroscopic variability. In this paper, the first of a series, we present Optical Gravitational Lensing Experiment (OGLE) light curves of all the confirmed symbiotic stars in the Large Magellanic Cloud, with one exception. By careful visual inspection and combined time series analysis techniques, we investigate for the first time in a systematic way the photometric properties of these astrophysical objects, trying in particular to distinguish the nature of the cool component (e.g. semiregular Variable versus OGLE small-amplitude red giant), to provide its first-order pulsational ephemerides and to link all this information with the physical parameters of the binary system as a whole. Among the most interesting results, there is the discovery of a 20 yr-long steady fading of Sanduleak's star, a peculiar symbiotic star known to produce the largest stellar jet ever discovered. We discuss by means of direct examples the crucial need for long-term multi-band observations to get a real understanding of symbiotic and other interacting binary stars. We eventually introduce BOMBOLO, a multi-band simultaneous imager for the Southern Astrophysical Research 4 m Telescope, whose design and construction we are currently leading.

Context. Near-infrared data on classical novae contain useful information about the ejected gas m... more Context. Near-infrared data on classical novae contain useful information about the ejected gas mass and the thermal emission by dust formed during eruption, and provide independent methods to classify the objects according to the colour of their progenitors, and the fading rate and features seen after eruption. The VISTA Variables in the Vía Láctea survey (VVV) is a near-IR ESO Public Survey mapping the Milky Way bulge and southern plane. Data taken during 2010-2011 covered the entire area in the JHKs bands plus some epochs in Ks-band of the ongoing VVV variability campaign.
Aims: We used the VVV data to create a near-IR catalogue of the known Galactic novae in the 562 sq. deg. area covered by VVV. We also compiled the information about novae from the variability tables of the VVV variability campaign.
Methods: We used the novae list provided by VSX/AAVSO catalogue to search for all objects within the VVV area. From the 140 novae, we were able to retrieve the JHKs colours of 93 objects. We also checked in the ongoing VVV variability campaign for the light curves of novae that erupted in the last years.
Results: The VVV near-IR catalogue of novae contains JHKs photometry of 93 objects completed as of December 2012. VVV allows to monitor objects within up to ΔKs ~ 10 mag range. VVV images can also be used to discover and study novae by searching for the expanding shell. Since objects are seen at different distances and reddening levels, the colour-magnitude and colour-colour diagrams show the novae spread in magnitude as well as in colour. Dereddened colours and reddening-free indices were used with caution and cannot be a good approach in all cases since the distance and spectral features prevent more conclusive results for some extreme objects. Light curves for some recent novae are presented.
Conclusions: Thanks to its high spatial resolution in the near IR and wide Ks-range, the VVV survey can be a major contributor to the search for and study of novae in the most crowded and high-extinction regions of the Milky Way. The VVV survey area contains ~35% of all known novae in the Galaxy.
Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002.

We present photometric and spectroscopic analysis of AE For - a detached eclipsing binary compose... more We present photometric and spectroscopic analysis of AE For - a detached eclipsing binary composed of two late K dwarfs. The masses of the components are found to be 0.6314 ± 0.0035 and 0.6197 ± 0.0034 M⊙ and the radii to be 0.67 ± 0.03 and 0.63 ± 0.03 R⊙ for primary and secondary component, respectively. Both components are significantly oversized compared to theoretical models, which we attribute to their high activity. They show Hα, Hβ, Hγ, Ca H and Ca K in emission, and are heavily spotted, causing large variations of the light curve.

We report on the discovery of large-amplitude flickering from V648 Car (= SS73-17), a poorly stud... more We report on the discovery of large-amplitude flickering from V648 Car (= SS73-17), a poorly studied object listed among the very few hard X-ray-emitting symbiotic stars. We performed millimagnitude precision optical photometry with the Swope Telescope at the Las Campanas Observatory, Chile, and found that V648 Car shows large U-band variability over timescales of minutes. To our knowledge, it exhibits some of the largest flickering of a symbiotic star ever reported. Our finding supports the hypothesis that symbiotic white dwarfs producing hard X-rays are predominantly powered by accretion, rather than quasi-steady nuclear burning, and have masses close to the Chandrasekhar limit. No significant periodicity is evident from the flickering light curve. The All Sky Automated Survey long-term V light curve suggests the presence of a tidally distorted giant accreting via Roche lobe overflow, and a binary period of ~520 days. On the basis of the outstanding physical properties of V648 Car as hinted at by its fast and long-term optical variability, as well as by its nature as a hard X-ray emitter, we therefore call for simultaneous follow-up observations in different bands, ideally combined with time-resolved optical spectroscopy.

Context. The ESO public survey VISTA variables in the Vía Láctea (VVV) started in 2010. VVV targe... more Context. The ESO public survey VISTA variables in the Vía Láctea (VVV) started in 2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane region and is expected to run for about five years.
Aims: We describe the progress of the survey observations in the first observing season, the observing strategy, and quality of the data obtained.
Methods: The observations are carried out on the 4-m VISTA telescope in the ZYJHKs filters. In addition to the multi-band imaging the variability monitoring campaign in the Ks filter has started. Data reduction is carried out using the pipeline at the Cambridge Astronomical Survey Unit. The photometric and astrometric calibration is performed via the numerous 2MASS sources observed in each pointing.
Results: The first data release contains the aperture photometry and astrometric catalogues for 348 individual pointings in the ZYJHKs filters taken in the 2010 observing season. The typical image quality is 0.9 arcsec {-1.0 arcsec}. The stringent photometric and image quality requirements of the survey are satisfied in 100% of the JHKs images in the disk area and 90% of the JHKs images in the bulge area. The completeness in the Z and Y images is 84% in the disk, and 40% in the bulge. The first season catalogues contain 1.28 × 108 stellar sources in the bulge and 1.68 × 108 in the disk area detected in at least one of the photometric bands. The combined, multi-band catalogues contain more than 1.63 × 108 stellar sources. About 10% of these are double detections because of overlapping adjacent pointings. These overlapping multiple detections are used to characterise the quality of the data. The images in the JHKs bands extend typically 4 mag deeper than 2MASS. The magnitude limit and photometric quality depend strongly on crowding in the inner Galactic regions. The astrometry for Ks = 15-18 mag has rms 35-175 mas.
Conclusions: The VVV Survey data products offer a unique dataset to map the stellar populations in the Galactic bulge and the adjacent plane and provide an exciting new tool for the study of the structure, content, and star-formation history of our Galaxy, as well as for investigations of the newly discovered star clusters, star-forming regions in the disk, high proper motion stars, asteroids, planetary nebulae, and other interesting objects.
Based on observations taken within the ESO VISTA Public Survey VVV, Programme ID 179.B-2002.

Highly collimated gas ejections are among the most dramatic structures in the universe, observed ... more Highly collimated gas ejections are among the most dramatic structures in the universe, observed to emerge from very different astrophysical systems—from active galactic nuclei down to young brown dwarf stars. Even with the huge span in spatial scales, there is convincing evidence that the physics at the origin of the phenomenon, namely, the acceleration and collimation mechanisms, is the same in all classes of jets. Here we report on the discovery of a giant, highly collimated jet from Sanduleak's star in the Large Magellanic Cloud (LMC). With a physical extent of 14 pc at the distance of the LMC, it represents the largest stellar jet ever discovered, and the first resolved stellar jet beyond the Milky Way. The kinematics and extreme chemical composition of the ejecta from Sanduleak's star bear strong resemblance with the low-velocity remnants of SN1987A and with the outer filaments of the most famous supernova progenitor candidate, η Carinae. Moreover, the precise knowledge of the jets distance implies that it will be possible to derive accurate estimates of most of its physical properties. Sanduleak's bipolar outflow will thus become a crucial test bed for future theoretical modeling of astrophysical jets.

Aims: We are performing a search for symbiotic stars using IPHAS, the INT Hα survey of the northe... more Aims: We are performing a search for symbiotic stars using IPHAS, the INT Hα survey of the northern Galactic plane, and follow-up observations.
Methods: Candidate symbiotic stars are selected on the basis of their IPHAS and near-IR colours, and spectroscopy and photometry are obtained to determine their nature. We present here observations of the symbiotic star candidate IPHAS J205836.43+503307.2.
Results: The optical spectrum shows the combination of a number of emission lines, among which are the high-excitation species of [O iii], He ii, [Ca v], and [Fe vii], and a red continuum with the features of a star at the cool end of the carbon star sequence. The nebular component is spatially resolved: the analysis of the spatial profile of the [N ii]6583 line in the spectrum indicates a linear size of ~ 2.5 arcsec along the east-west direction. Its velocity structure suggests an aspherical morphology. The near-infrared excess of the source, which was especially strong in 1999, indicated that a thick circumstellar dust shell was also present in the system. The carbon star has brightened in the last decade by two to four magnitudes at red and near-infrared wavelengths. Photometric monitoring during a period of 60 days from November 2010 to January 2011 reveals a slow luminosity decrease of 0.2 mag.
Conclusions: From the observed spectrophotometric properties and variability, we conclude that the source is a new Galactic symbiotic star of the D-type, of the rare kind that contains a carbon star, likely a carbon Mira. Only two other systems of this type are known in the Galaxy.
Based on observations obtained with the 2.5 m INT and the 4.2 m WHT telescopes of the Isaac Newton Group of Telescopes and the 1.5 m Carlos Sanchez Telescope, operating on the islands of La Palma and Tenerife at the Spanish Observatories of the Roque de Los Muchachos and Teide of the Instituto de Astrofísica de Canarias; the 2.1 m telescope at San Pedro Martir, Mexico; and the GAPC 0.7 m Ritchey-Chrétien telescope at La Polse di Cougnes, Udine, Italy.

The VISTA Variables in the Via Lactea (VVV) is an ESO public near-IR variability survey that is s... more The VISTA Variables in the Via Lactea (VVV) is an ESO public near-IR variability survey that is scanning the Milky Way bulge and an adjacent section of the Galactic mid-plane. The survey will take 1929 hours of observations with the VISTA 4.1-m telescope during five years, covering a billion point sources across an area of 520 sqdeg, including 36 known globular clusters and more than 350 open clusters. The final product will be a deep IR atlas in five passbands (0.9 - 2.5 microns) and a catalogue of more than a million variable point sources.

We have collected continuum data of a sample of D-type symbiotic stars. By modelling their spectr... more We have collected continuum data of a sample of D-type symbiotic stars. By modelling their spectral energy distribution in a colliding-wind theoretical scenario we have found characteristics common to all the systems: (1) at least two dust shells are clearly present, one at ~1000K and the other at ~400K they dominate the emission in the infrared; (2) the radio data are explained by thermal self-absorbed emission from the reverse shock between the stars; while (3) the data in the long wavelength tail come from the expanding shock outwards the system; (4) in some symbiotic stars, the contribution from the white dwarf in the UV is directly seen. Finally, (5) for some objects soft X-ray emitted by bremsstrahlung downstream of the reverse shock between the stars is predicted. The results thus confirm the validity of the colliding-wind model and the important role of the shocks. The comparison of the fluxes calculated at the nebula with those observed at the Earth reveals the distribution throughout the system of the different components, in particular the nebulae and the dust shells. The correlation of shell radii with the orbital period shows that larger radii are found at larger periods. Moreover, the temperatures of the dust shells regarding the sample are found at ~1000 and <=400K, while in the case of late giants they spread more uniformly throughout the same range.

We investigate the symbiotic star BI Crucis (BI Cru) through a comprehensive and self-consistent ... more We investigate the symbiotic star BI Crucis (BI Cru) through a comprehensive and self-consistent analysis of the spectra emitted in three different epochs: 1960s, 1970s and late 1980s. In particular, we would like to find out the physical conditions in the shocked nebula and in the dust shells, as well as their location within the symbiotic system, by exploiting both photometric and spectroscopic data from radio to UV. We suggest a model which, on the basis of optical imaging, emission-line ratios and spectral energy distribution profile, is able to account for collision of the winds, formation of lobes and jets by accretion onto the white dwarf (WD), as well as for the interaction of the blast wave from a past, unrecorded outburst with the interstellar medium (ISM). We have found that the spectra observed throughout the years show the marks of the different processes at work within BI Cru, perhaps signatures of a post-outburst evolution. We then call for new infrared and millimeter observations, potentially able to resolve the inner structure of the symbiotic nebula.

Aims:We present a comprehensive and self-consistent modelling of the D' type symbiotic star (SS) ... more Aims:We present a comprehensive and self-consistent modelling of the D' type symbiotic star (SS) HD 330036 from radio to UV.
Methods: Within a colliding-wind scenario, we analyse the continuum, line, and dust spectra by means of SUMA, a code that simulates the physical conditions of an emitting gaseous cloud under the coupled effect of ionisation from an external radiation source and shocks.
Results: We find that the UV lines are emitted from high-density gas between thestars downstream of the reverse shock, while the optical lines are emitted downstream of the shock propagating outwards from the system. As regards the continuum SED, three shells are identified in the IR, at 850 K, 320 K, and 200 K with radii r = 2.8 × 1013 cm, 4 × 1014 cm, and 1015 cm, respectively, after adopting a distance to Earth of d=2.3 kpc. Interestingly, all these shells appear to be circumbinary. Analysis of the unexploited ISO-SWS spectrum reveals that both PAHs and crystalline silicates coexist in HD 330036, with PAHs associated to the internal shell at 850 K, and crystalline silicates stored in the cool shells at 320 K and 200 K. Strong evidence that crystalline silicates are shaped in a disk-like structure is derived on the basis of the relative band strengths. Finally, we suggest that shocks can be a reliable mechanism for activating the annealing and the consequent crystallisation processes.
Conclusions: We show that a consistent interpretation of gas and dust spectra emitted by SS can be obtained by models that account for the coupled effect of the photoionising flux and of shocks. The VLTI/MIDI proposal recently accepted by ESO aims to verify and better constrain some of our results by means of IR interferometric observations.

Aims:In this paper, we analyse the spectra of D-type SS H1-36 within a colliding-wind scenario. W... more Aims:In this paper, we analyse the spectra of D-type SS H1-36 within a colliding-wind scenario. We aim to analyse the properties of this object by taking the observational data along the whole electromagnetic spectrum into account, in order to derive a self-consistent picture able to interpret the nature of the system as a whole.
Methods: After constraining the relative physical conditions by modelling more than 40 emission lines from radio to UV, we are able to explain the continuum spectral energy distribution by considering all the emitting contributions arising from both the stars, the dust shells, and the gaseous nebulæ.
Results: A comprehensive model of the radio spectra allows reproduction of the different slopes of the radio profile and the turnover frequency, as well as the different sizes of the observed shocked envelope at different frequencies in the light of the contributions from the expanding and reverse nebulæ. The IR continuum unveils the presence of two dust shells with different radii and temperatures, which might be a distinctive feature of D-type symbiotic systems as a class of objects. The broad profiles of IR lines direct us to investigate whether an X-ray jet may be present.
Conclusions: This insight leads us to indicate H1-36 as a promising X-ray target and to encourage observations and studies that consistently take the complex nature of symbiotic stars into account throughout the whole electromagnetic spectrum.

Proceedings of the International Astronomical Union, 2012