arXiv subjects

Cecilia Mateu

Publications and source records attributed to Cecilia Mateu.

33 records · Page 2Linked to original sources

arXiv2018

The Galactic Thick Disc density profile traced with RR Lyrae stars

We used a combination of public RR Lyrae star catalogs and a Bayesian methodology to derive robust structural parameters of the inner Halo (<25 kpc) and Thick Disc of the Milky Way. RR Lyrae stars are an unequivocal tracer of old metal-poor populations, for which accurate distances and extinctions can be individually estimated and so, are a reliable independent means of tracing the population of the old high-[α/Fe] disc usually associated to the Thick Disc. In particular, the chosen RR Lyrae sample spans regions at low galactic latitude toward the anti-center direction, allowing to probe the outermost parts of the disc. Our results favour a Thick Disc with short scale height and short scale length, $h_z=0.65_{-0.05}^{+0.09}$ kpc, $h_R=2.1_{-0.25}^{+0.82}$ kpc, for a model in which the inner Halo has a constant flattening of $q=0.90_{-0.03}^{+0.05}$ and a power law index of $n=-2.78_{-0.05}^{+0.05}$. Similar short scales for the Thick Disc are also found when considering an inner Halo with flattening dependent on radius. We also explored a model in which the Thick Disc has a flare and, although this is only mildly constrained by our data, a flare onset in the inner $\sim11$ kpc is highly disfavoured.

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arXiv2018

The CIDA Variability Survey of Orion OB1 II: demographics of the young, low-mass stellar populations

We present results of our large scale, optical, multi-epoch photometric survey of ~180 square degrees across the Orion OB1 association, complemented with extensive follow up spectroscopy. We map and characterize in an uniform way the off-cloud, low-mass, pre-main sequence populations. We report 2064, mostly K and M-type, confirmed T Tauri members. Most (59%) are located in the OB1a subassociation, 27% in OB1b, and 14% within the confines of the A and B molecular clouds. There is significant structure in the spatial distribution of the young stars. We characterize two new clusterings of T Tauri stars, HD 35762 and HR 1833 in the OB1a subassociation, and two stellar overdensities in OB1b. There is indication of two populations of young stars in the OB1b region, located at two different distances, which may be due to the OB1a subassociation overlapping on front of OB1b. The various groups and regions can be ordered in an age sequence that agrees with the long standing picture of star formation starting in Orion OB1a some 10-15 Myr ago. We define a new type of T Tauri star, the C/W class, objects we propose may be nearing the end of their accretion phase. We detect the observational signature of Li depletion in young K and M stars with a timescale of 8.5 Myr. The decline of the accretion fraction from ~2 - 10 Myr, implies an accretion e-folding timescale of 2.1 Myr. Finally, the median amplitude of the V-band variability shows the decline of stellar activity, from accreting Classical T Tauri stars to the least active field dwarfs.

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arXiv2017

Fourteen candidate RR Lyrae star streams in the inner Galaxy

We apply the GC3 stream-finding method to RR Lyrae stars (RRLS) in the Catalina survey. We find two RRLS stream candidates at $>4σ$ confidence and another 12 at $>3.5σ$ confidence over the Galactocentric distance range $4 < D/{\rm kpc} < 26$. Of these, only two are associated with known globular clusters (NGC 1261 and Arp2). The remainder are candidate `orphan' streams, consistent with the idea that globular cluster streams are most visible close to dissolution. Our detections are likely a lower bound on the total number of dissolving globulars in the inner galaxy, since many globulars have few RRLS while only the brightest streams are visible over the Galactic RRLS background, particularly given the current lack of kinematical information. We make all of our candidate streams publicly available and provide a new GALSTREAMS Python library for the footprints of all known streams and overdensities in the Milky Way.

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arXiv2017

Predictions for the detection of Tidal Streams with Gaia using Great Circle Methods

The Gaia astrometric mission may offer an unprecedented opportunity to discover new tidal streams in the Galactic halo. To test this, we apply nGC3, a great-circle-cell count method that combines position and proper motion data to identify streams, to ten mock Gaia catalogues of K giants and RR Lyrae stars constructed from cosmological simulations of Milky Way analogues. We analyse two sets of simulations, one using a combination of $N$-body and semi-analytical methods which has extremely high resolution, the other using hydro-dynamical methods, which captures the dynamics of baryons, including the formation of an in situ halo. These ten realisations of plausible Galactic merger histories allow us to assess the potential for the recovery of tidal streams in different Milky Way formation scenarios. We include the Gaia~selection function and observational errors in these mock catalogues. We find that the nGC3 method has a well-defined detection boundary in the space of stream width and projected overdensity, that can be predicted based on direct observables alone. We predict that about 4-13 dwarf galaxy streams can be detected in a typical Milky Way-mass halo with Gaia+nGC3, with an estimated efficiency of $>$80\% inside the detection boundary. The progenitors of these streams are in the mass range of the classical dwarf galaxies and may have been accreted as early as redshift $\sim3$. Finally, we analyse how different possible extensions of the Gaia mission will improve the detection of tidal streams.

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arXiv2016

The Astropy Problem

The Astropy Project (http://astropy.org) is, in its own words, "a community effort to develop a single core package for Astronomy in Python and foster interoperability between Python astronomy packages." For five years this project has been managed, written, and operated as a grassroots, self-organized, almost entirely volunteer effort while the software is used by the majority of the astronomical community. Despite this, the project has always been and remains to this day effectively unfunded. Further, contributors receive little or no formal recognition for creating and supporting what is now critical software. This paper explores the problem in detail, outlines possible solutions to correct this, and presents a few suggestions on how to address the sustainability of general purpose astronomical software.

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arXiv2016

The rotation period distributions of 4--10 Myr T Tauri stars in Orion OB1: New constraints on pre-main-sequence angular momentum evolution

Most existing studies of the angular momentum evolution of young stellar populations have focused on the youngest (1-3 Myr) T Tauri stars. In contrast, the angular momentum distributions of older T Tauri stars (4-10 Myr) have been less studied, even though they hold key insight to understanding stellar angular momentum evolution at a time when protoplanetary disks have largely dissipated and when models therefore predict changes in the rotational evolution that can in principle be tested. We present a study of photometric variability among 1,974 confirmed T Tauri members of various sub-regions of the Orion OB1 association, and with ages spanning 4-10 Myr, using optical time-series from three different surveys. For 564 of the stars (~32% of the weak-lined T Tauri stars and ~13% of the classical T Tauri stars in our sample) we detect statistically significant periodic variations which we attribute to the stellar rotation periods, making this one of the largest samples of T Tauri star rotation periods yet published. We observe a clear change in the overall rotation period distributions over the age range 4-10 Myr, with the progressively older sub-populations exhibiting systematically faster rotation. This result is consistent with angular momentum evolution model predictions of an important qualitative change in the stellar rotation periods starting at ~5 Myr, an age range for which very few observational constraints were previously available.

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arXiv2015

Detection of satellite remnants in the Galactic Halo with Gaia III. Detection limits for Ultra Faint Dwarf Galaxies

We present a method to identify Ultra Faint Dwarf Galaxy (UFDG) candidates in the halo of the Milky Way using the future Gaia catalogue and we explore its detection limits and completeness. The method is based on the Wavelet Transform and searches for over-densities in the combined space of sky coordinates and proper motions, using kinematics in the search for the first time. We test the method with a Gaia mock catalogue that has the Gaia Universe Model Snapshot (GUMS) as a background, and use a library of around 30 000 UFDGs simulated as Plummer spheres with a single stellar population. For the UFDGs we use a wide range of structural and orbital parameters that go beyond the range spanned by real systems, where some UFDGs may remain undetected. We characterize the detection limits as function of the number of observable stars by Gaia in the UFDGs with respect to that of the background and their apparent sizes in the sky and proper motion planes. We find that the addition of proper motions in the search improves considerably the detections compared to a photometric survey at the same magnitude limit. Our experiments suggest that Gaia will be able to detect UFDGs that are similar to some of the known UFDGs even if the limit of Gaia is around 2 magnitudes brighter than that of SDSS, with the advantage of having a full-sky catalogue. We also see that Gaia could even find some UFDGs that have lower surface brightness than the SDSS limit.

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arXiv2015

The number fraction of discs around brown dwarfs in Orion OB1a and the 25 Orionis group

We present a study of 15 new brown dwarfs belonging to the $\sim7$ Myr old 25 Orionis group and Orion OB1a sub-association with spectral types between M6 and M9 and estimated masses between $\sim0.07$M$_\odot$ and $\sim0.01$ M$_\odot$. By comparing them through a Bayesian method with low mass stars ($0.8\lesssim$ M/M$_\odot\lesssim0.1$) from previous works in the 25 Orionis group, we found statistically significant differences in the number fraction of classical T Tauri stars, weak T Tauri stars, class II, evolved discs and purely photospheric emitters at both sides of the sub-stellar mass limit. Particularly we found a fraction of $3.9^{+2.4}_{-1.6}~\%$ low mass stars classified as CTTS and class II or evolved discs, against a fraction of $33.3^{+10.8}_{-9.8}~\%$ in the sub-stellar mass domain. Our results support the suggested scenario in which the dissipation of discs is less efficient for decreasing mass of the central object.

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arXiv2015

On the recovery of galaxy properties from SED fitting solutions

We explore the ability of four different inverse population synthesis codes to recover the physical properties of galaxies from their spectra by SED fitting. Three codes, DynBaS, TGASPEX, and GASPEX, have been implemented by the authors and are described in detail in the paper. STARLIGHT, the fourth code, is publicly available. DynBaS selects dynamically a different spectral basis to expand the spectrum of each target galaxy; TGASPEX uses an unconstrained age basis, whereas GASPEX and STARLIGHT use for all fits a fixed spectral basis selected a priori by the code developers. Variable and unconstrained basis reflect the peculiarities of the fitted spectrum and allow for simple and robust solutions to the problem of extracting galaxy parameters from spectral fits. We assemble a Synthetic Spectral Atlas of Galaxies (SSAG), comprising 100,000 galaxy spectra corresponding to an equal number of star formation histories based on the recipe of Chen et al. (2012). We select a subset of 120 galaxies from SSAG with a colour distribution similar to that of local galaxies in the seventh data release (DR7) of the Sloan Digital Sky Survey (SDSS) and produce 30 random noise realisations for each of these spectra. For each spectrum we recover the mass, mean age, metallicity, internal dust extinction, and velocity dispersion characterizing the dominant stellar population in the problem galaxy. All methods produce almost perfect fits to the target spectrum, but the recovered physical parameters can differ significantly. Our tests provide a quantitative measure of the accuracy and precision with which these parameters are recovered by each method. From a statistical point of view all methods yield similar precisions, whereas DynBaS produces solutions with minimal systematic biases in the distributions of residuals for all of these parameters.

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arXiv2014

The low mass star and sub-stellar populations of the 25 Orionis group

We present the results of a survey of the low mass star and brown dwarf population of the 25 Orionis group. Using optical photometry from the CIDA Deep Survey of Orion, near IR photometry from the Visible and Infrared Survey Telescope for Astronomy and low resolution spectroscopy obtained with Hectospec at the MMT, we selected 1246 photometric candidates to low mass stars and brown dwarfs with estimated masses within $0.02 \lesssim M/M_\odot \lesssim 0.8$ and spectroscopically confirmed a sample of 77 low mass stars as new members of the cluster with a mean age of $\sim$7 Myr. We have obtained a system initial mass function of the group that can be well described by either a Kroupa power-law function with indices $α_3=-1.73\pm0.31$ and $α_2=0.68\pm0.41$ in the mass ranges $0.03\leq M/M_\odot\leq 0.08$ and $0.08\leq M/M_\odot\leq0.5$ respectively, or a Scalo log-normal function with coefficients $m_c=0.21^{+0.02}_{-0.02}$ and $σ=0.36\pm0.03$ in the mass range $0.03\leq M/M_\odot\leq0.8$. From the analysis of the spatial distribution of this numerous candidate sample, we have confirmed the East-West elongation of the 25 Orionis group observed in previous works, and rule out a possible southern extension of the group. We find that the spatial distributions of low mass stars and brown dwarfs in 25 Orionis are statistically indistinguishable. Finally, we found that the fraction of brown dwarfs showing IR excesses is higher than for low mass stars, supporting the scenario in which the evolution of circumstellar discs around the least massive objects could be more prolonged.

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arXiv2012

The QUEST RR Lyrae Survey: III. The Low Galactic Latitude Catalogue

We present results for the QUEST RR Lyrae Survey at low galactic latitude, conducted entirely with observations obtained with the QUEST mosaic camera and the 1.0/1.5m Jürgen Stock Schmidt telescope at the National Observatory of Venezuela. The survey spans an area of 476 sq. deg on the sky, with multi-epoch observations in the V, R and I photometric bands for 6.5x10^6 stars in the galactic latitude range 30<= b(deg) <=+25, in a direction close to the Galactic Anticenter 190<= l(deg)<= 230. The variability survey has a typical number of 30 observations per object in V and I and ~25 in R, with up to ~120-150 epochs in V and I and up to ~100 in R in the best sampled regions. The completeness magnitudes of the survey are V=R=18.5 mag, and I=18.0 mag. We identified 211 RR Lyrae stars, 160 bona fide stars of type ab and 51 candidates of type c, ours being the first deep RR Lyrae survey conducted at low galactic latitude.The completeness of the RR Lyrae survey was estimated in >95 per cent and ~85 per cent for RRab and RRc stars respectively. Photometric metallicities were computed based on the light curves and individual extinctions calculated from minimum light colours for each RRab star. Distances were obtained with typical errors ~7 per cent. The RR Lyrae survey simultaneously spans a large range of heliocentric distances 0.5<= R_hel(kpc)<=40 and heights above the plane -15<=z(kpc)<=+20, with well known completeness across the survey area, making it an ideal set for studying the struc ture of the Galactic thick disk.

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arXiv2011

Detection of Satellite Remnants in the Galactic Halo with Gaia - II. A modified Great Circle Cell Method

We propose an extension of the GC3 streamer finding method of Johnston et al. 1996 that can be applied to the future Gaia database. The original method looks for streamers along great circles in the sky, our extension adds the kinematical restriction that velocity vectors should also be constrained to lie along these great circles, as seen by a Galactocentric observer. We show how to use these combined criteria starting from heliocentric observables. We test it by using the mock Gaia catalogue of Brown et al. 2005, which includes a realistic Galactic background and observational errors, but with the addition of detailed star formation histories for the simulated satellites. We investigate its success rate as a function of initial satellite luminosity, star formation history and orbit. We find that the inclusion of the kinematical restriction vastly enhances the contrast between a streamer and the background, even in the presence of observational errors, provided we use only data with good astrometric quality (fractional errors of 30 per cent or better). The global nature of the method diminishes the erasing effect of phase mixing and permits the recovery of merger events of reasonable dynamical age. Satellites with a star formation history different to that of the Galactic background are also better isolated. We find that satellites in the range of 10^8-10^9 Lsun can be recovered even for events as old as ~10 Gyr. Even satellites with 4-5x10^7 Lsun can be recovered for certain combinations of dynamical ages and orbits.

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arXiv2009

No Excess of RR Lyrae Stars in the Canis Major Overdensity

Our multi-epoch survey of ~20 sq. deg. of the Canis Major overdensity has detected only 10 RR Lyrae stars (RRLS). We show that this number is consistent with the number expected from the Galactic halo and thick disk populations alone, leaving no excess that can be attributed to the dwarf spheroidal (dSph) galaxy that some authors have proposed as the origin of the CMa overdensity. If this galaxy resembles the dSph satellites of the Milky Way and of M31 and has the putative Mv~-14.5, our survey should have detected several tens of RRLS. Even if Mv<-12, the expected excess is >10, which is not observed. Either the old stellar population of this galaxy has unique properties or, as others have argued before, the CMa overdensity is produced by the thin and thick disk and spiral arm populations of the Milky Way and not by a collision with a dSph satellite galaxy.

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arXiv2008

Spectroscopy of Bright QUEST RR Lyrae Stars: Velocity Substructures toward Virgo

Using a sample of 43 bright (V<16.1, distance <13 kpc) RR Lyrae stars (RRLS) from the QUEST survey with spectroscopic radial velocities and metallicities, we find that several separate halo substructures contribute to the Virgo overdensity (VOD). While there is little evidence for halo substructure in the spatial distribution of these stars, their distribution in radial velocity reveals two moving groups. These results are reinforced when the sample is combined with a sample of blue horizontal branch stars that were identified in the SDSS, and the combined sample provides evidence for one additional moving group. These groups correspond to peaks in the radial velocity distribution of a sample of F type main-sequence stars that was recently observed in the same directon by SEGUE, although in one case the RRLS and F star groups may not lie at the same distance. One of the new substructures has a very narrow range in metallicity, which is more consistent with it being the debris from a destroyed globular cluster than from a dwarf galaxy. A small concentration of stars have radial velocities that are similar to the Virgo Stellar Stream (VSS) that was identified previously in a fainter sample of RRLS. Our results suggest that this feature extends to distances as short as ~12 kpc from its previous detection at ~19 kpc. None of the new groups and only one star in the sample have velocities that are consistent with membership in the leading tidal stream from the Sagittarius Dwarf Spheroidal Galaxy, which some authors have suggested is the origin of the VOD.

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arXiv2007

Searching for RR Lyrae stars in the Canis Major Overdensity

The Canis Major overdensity (CMa) was initially proposed to be the remnant of a tidally disrupting dSph galaxy. Since its nature is still subject of debate, the goal of the present work was to conduct a large-scale RR Lyrae survey in CMa, in order to see if there is an overdensity of these stars. The survey spans a total area of ~34 sq. deg. with observations in V and R filters, made with the 1.0m Jurgen Stock Schmidt telescope at the National Astronomical Observatory of Venezuela. Current results in a subregion, including spectroscopic observations, show that the small number of RR Lyrae stars found can be accounted for by the halo and thick disk components of our Galaxy.

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