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A. Cabrera-Lavers

Publications and source records attributed to A. Cabrera-Lavers.

At least 73 records · Page 4Linked to original sources
arXiv2010

Transformations between 2MASS, SDSS and BVI photometric systems for late-type giants

We present colour transformations from Two Micron All Sky Survey (2MASS) photometric system to Johnson-Cousins system and to Sloan Digital Sky Survey (SDSS) system for late-type giants and vice versa. The giant star sample was formed using surface gravity constraints ($2 < \log g \leq 3$) to Cayrel de Strobel et al.\rq s (2001) spectroscopic catalogue. 2MASS, SDSS and Johnson-Cousins photometric data was taken from Cutri et al. (2003), Ofek (2008) and van Leeuwen (2007), respectively. The final sample was refined applying the following steps: (1) the data were dereddened, (2) the sample stars selected are of the highest photometric quality. We give two--colour dependent transformations as a function of metallicity as well as independent of metallicity. The transformations provide absolute magnitudes and distance determinations which can be used in space density evaluations at relatively short distances where some or all of the SDSS magnitudes of late-type giants are saturated.

astro-ph.SR↗
arXiv2010

Water-ice driven activity on Main-Belt Comet P/2010 A2 (LINEAR) ?

The dust ejecta of Main-Belt Comet P/2010 A2 (LINEAR) have been observed with several telescopes at the at the Observatorio del Roque de los Muchachos on La Palma, Spain. Application of an inverse dust tail Monte Carlo method to the images of the dust ejecta from the object indicates that a sustained, likely water-ice driven, activity over some eight months is the mechanism responsible for the formation of the observed tail. The total amount of dust released is estimated to be 5E7 kg, which represents about 0.3% of the nucleus mass. While the event could have been triggered by a collision, this cannot be decided from the currently available data.

astro-ph.EP↗
arXiv2009

SDSS Absolute Magnitudes for Thin Disc Stars based on Trigonometric Parallaxes

We present a new luminosity-colour relation based on trigonometric parallaxes for thin disc main-sequence stars in SDSS photometry. We matched stars from the newly reduced Hipparcos catalogue with the ones taken from 2MASS All-Sky Catalogue of Point Sources, and applied a series of constraints, i.e. relative parallax errors ($σ_π/π\leq0.05$), metallicity ($-0.30\leq[M/H]\leq0.20$ dex), age ($0\leq t \leq 10$ Gyr) and surface gravity ($\log g>4$), and obtained a sample of thin disc main-sequence stars. Then, we used our previous transformation equations (Bilir et al. 2008a) between SDSS and 2MASS photometries and calibrated the $M_{g}$ absolute magnitudes to the $(g-r)_{0}$ and $(r-i)_0$ colours. The transformation formulae between 2MASS and SDSS photometries along with the absolute magnitude calibration provide space densities for bright stars which saturate the SDSS magnitudes.

astro-ph.GA↗
arXiv2008

The long Galactic bar as seen by UKIDSS Galactic Plane Survey

Over the last decade there have been a series of results supporting the hypothesis of the existence of a long thin bar in the Milky Way with a half-length of 4.5 kpc and a position angle of around 45 deg. This is apparently a very different structure from the triaxial bulge of the Galaxy, which is thicker and shorter and dominates the star counts at |l|<10 deg. In this paper, we analyse the stellar distribution in the inner Galaxy to see if there is clear evidence for two triaxial or bar-like structures in the Milky Way. By using the red-clump population as a tracer of Galactic structure, we determine the apparent morphology of the inner Galaxy. Deeper and higher spatial resolution NIR photometry from the UKIDSS Galactic Plane Survey allows us to use in-plane data even at the innermost Galactic longitudes, a region where the source confusion is a dominant effect that makes it impossible to use other NIR databases such as 2MASS or TCS-CAIN. We show that results previously obtained with using the red-clump giants are confirmed with the in-plane data from UKIDSS GPS. There are two different structures coexisting in the inner Galactic plane: one with a position angle of 23.60+-2.19 deg that can be traced from the Galactic Centre up to l=10 deg (the Galactic bulge), and other with a larger position angle of 42.44+-2.14 deg, that ends around l=28 deg (the long Galactic bar).

astro-ph↗
arXiv2008

Luminosity-Colours relations for thin disc main-sequence stars

In this study we present the absolute magnitude calibrations of thin disc main-sequence stars in the optical ($M_{V}$), and in the near-infrared ($M_{J}$). Thin disc stars are identified by means of Padova isochrones, and absolute magnitudes for the sample are evaluated via the newly reduced Hipparcos data. The obtained calibrations cover a large range of spectral types: from A0 to M4 in the optical and from A0 to M0 in the near-infrared. Also, we discuss the of effects binary stars and evolved stars on the absolute magnitude calibrations. The usage of these calibrations can be extended to the estimation of galactic model parameters for the thin disc individually, in order to compare these parameters with the corresponding ones estimated by $χ{^2}_{min}$ statistics (which provides galactic model parameters for thin and thick discs, and halo simultaneously) to test any degeneracy between them. The calibrations can also be used in other astrophysical researches where distance plays an important role in that study.

astro-ph↗
arXiv2008

Estimation of galactic model parameters in high latitudes with SDSS

We estimated the Galactic model parameters for a set of 36 high-latitude fields included in the currently available Data Release 5 (DR 5) of the Sloan Digital Sky Survey ({\em SDSS}), to explore their possible variation with the Galactic longitude. The thick disc scaleheight moves from $\sim$550 pc at $120^{\circ}<l<150^{\circ}$ to $\sim$720 pc at $250^{\circ}<l<290^{\circ}$, while the thin disc scaleheight is as large as $\sim$195 pc in the anticenter direction and $\sim$15% lower at $|l|<30^\circ$. Finally, the axis ratio ($c/a$) of the halo changes from a mean value of $\sim$0.55 in the two first quadrants of the Galaxy to $\sim$0.70 at $190^{\circ}<l<300^{\circ}$. For the halo, the reason for the dependence of the model parameters on the Galactic longitude arises from the well known asymmetric structure of this component. However, the variation of the model parameters of the thin and thick discs with Galactic longitude originates from the gravitational effect of the Galactic long bar. Moreover, the excess of stars in quadrant I (quadrant III) over quadrant IV (quadrant II) is in agreement with this scenario.

astro-ph↗
arXiv2007

Metallicity distribution of red giants in the Inner Galaxy from Near Infrared spectra

In this paper, we present low resolution (R=500) near-infrared spectra for selected and serendipitous sources in six inner in-plane Galactic fields, with the aim of analysing the stellar content present. From the equivalent widths of the main features of the K band spectra (the NaI, CaI and CO bandheads) we have derived the metallicities of the sources by means of the empirical scale obtained by Ramírez et al. (2000) and Frogel et al. (2001) for luminous red giants. Our results show how the mean metallicity of the sample varies with Galactic longitude. We find two groups of stars, one whose [Fe/H] is similar to the values obtained for the bulge in other studies (Molla et al. 2000; Schultehis et al 2003), and a second one with a metallicity similar to that of the inner parts of the disc (Rocha-Pinto et al. 2006). The relative density of both groups of stars in our sample varies in a continuous way from the bulge to the disc. This could hint at the existence of a single component apart from the disc and bulge, running from l=7 to l=27 and able to transport disc stars inwards and bulge stars outwards, which could be the Galactic bar that has been detected in previous works as an overdensity of stars located at those galactic coordinates (Hammersley et al. 1994, 2000; Picaud et al. 2003).

astro-ph↗
arXiv2007

Transformations between 2MASS, SDSS and BVRI photometric systems: bridging the near infrared and optical

We present colour transformations for the conversion of the {\em 2MASS} photometric system to the Johnson-Cousins $UBVRI$ system and further into the {\em SDSS} $ugriz$ system. We have taken {\em SDSS} $gri$ magnitudes of stars measured with the 2.5-m telescope from $SDSS$ Data Release 5 (DR5), and $BVRI$ and $JHK_{s}$ magnitudes from Stetson's catalogue and \citet{Cu03}, respectively. We matched thousands of stars in the three photometric systems by their coordinates and obtained a homogeneous sample of 825 stars by the following constraints, which are not used in previous transformations: 1) the data are de-reddened, 2) giants are omitted, and 3) the sample stars selected are of the highest quality. We give metallicity, population type, and transformations dependent on two colours. The transformations provide absolute magnitude and distance determinations which can be used in space density evaluations at short distances where some or all of the {\em SDSS} $ugriz$ magnitudes are saturated. The combination of these densities with those evaluated at larger distances using {\em SDSS} $ugriz$ photometry will supply accurate Galactic model parameters, particularly the local space densities for each population.

astro-ph↗
arXiv2007

Reaffirming the connection between the Galactic stellar warp and the Canis Major overdensity

We perform a critical re-analysis and discussion of recent results presented in the literature which interpret the CMa overdensity as the signature of an accreting dwarf galaxy or a new substructure within the Galaxy. Several issues are addressed. We show that arguments against the ``warp'' interpretation are based on an erroneous perception of the Milky Way. There is nothing anomalous with colour--magnitude diagrams on opposite sides of the average warp mid-plane being different. We witnessed the rise and fall of the blue plume population, first attributed to young stars in a disrupting dwarf galaxy and now discarded as a normal disc population. Similarly, there is nothing anomalous in the outer thin+thick disc metallicities being low (-1<[Fe/H]<-0.5), and spiral arms (as part of the thin disc) should, and do, warp. Most importantly, we show unambiguously that, contrary to previous claims, the warp produces a stellar overdensity that is distance-compatible with that observed in CMa.The CMa over-density remains fully accounted for in a first order approach by Galactic models without new substructures. Given the intrinsic uncertainties (concerning the properties of the warp, flare and disc cutoff, the role of extinction and degeneracy), minor deviations with respect to these models are not enough to support the hypothesis of an accreted dwarf galaxy or new substructure within the Milky Way disc.

astro-ph↗
arXiv2007

The metallicity distributions in high-latitudes with SDSS

We present metallicities and their variations with different parameters for 36 high-latitude fields covering Galactic longitudes 0<l<360. The metallicities for relatively short vertical distances (z<2.5 kpc) show systematic fluctuations with Galactic longitude, similar to those of the thick-disc scaleheight, which may be interpreted as indicating a common origin, viz., the flare effect of the disc. This suggestion is supported by the metallicity variations which we find as functions of radial distance. The metallicity variation at larger vertical distances (6.5<z<9.5 kpc) is small but monotonic. Three different vertical metallicity gradients could be detected: d[M/H]/dz=-0.22(+/-0.03), d[M/H]/dz=-0.38 (+/-0.06), and d[M/H]/dz=-0.08 (+/-0.07) dex/kpc for the intervals z<3, 3<z<5, and 5<z<10 kpc, respectively. Since our data cover the whole Galactic longitude interval, the resulting metallicity gradients can be interpreted as properties of the larger-scale Galaxy. The first gradient confirms the dissipational formation of the disc at short z-distances. The steeper gradient corresponds to the transition region between different population components of the Galaxy, and finally, the lowest value provides an adequate description of the inner-halo metallicity gradient.

astro-ph↗
arXiv2007

Tracing the long bar with red-clump giants

Over the last decade a series of results have lent support to the hypothesis of the existence of a long thin bar in the Milky Way with a half-length of 4.5 kpc and a position angle of around 45 deg. This is apparently a very different structure from the triaxial bulge of the Galaxy. In this paper, we analyse the stellar distribution in the inner 4 kpc of the Galaxy to see if there is clear evidence for two triaxial or barlike structures, or whether there is only one. By using the red-clump population as a tracer of the structure of the inner Galaxy we determine the apparent morphology of the inner Galaxy. Star counts from 2MASS are used to provide additional support for this analysis. We show that there are two very different large-scale triaxial structures coexisting in the inner Galaxy: a long thin stellar bar constrained to the Galactic plane (|b|<2 deg) with a position angle of 43.1 +- 1.8 deg, and a distinct triaxial bulge that extends to at least |b|<7.5 deg with a position angle of 12.6 +- 3.2 deg. The scale height of the bar source distribution is around 100 pc, whereas for the bulge the value of this parameter is five times larger.

astro-ph↗
arXiv2006

Estimation of Galactic model parameters in high latitudes with 2MASS

In this paper, we try to find any dependence of the Galactic structural parameters with the Galactic longitude for either the thin disc or the thick disc of the Milky Way, that would indicate to possible inhomogeneities or asymmetries in those Galactic components. Galactic model parameters obtained using a set of 36 high-latitude fields with 2MASS photometry for the different fields show that, effectively, they are Galactic longitude-dependent. The thick disc scaleheight changes from 800 pc at 150 deg < l < 230 deg to 1050 pc at |l| < 30 deg. A plausible explanation for this finding might be the effect of the flare in this Galactic component that changes the scaleheight with Galactocentric distance

astro-ph↗
arXiv2006

The Long Bar in the Milky Way. Corroboration of an old hypothesis

Recent GLIMPSE data have further confirmed the hypothesis of the existence of an in-plane long bar different from the bulge of the Milky Way with the same characteristics as emphasized some years ago by our team. In this paper, we present two new analyses that corroborate recent and earlier claims concerning the existence in our Galaxy of a long flat bar with approximate dimensions 7.8 kpc x 1.2 kpc x 0.2 kpc and a position angle of approximately 43 deg.: 1) star counts with 2MASS All-Sky Release and MSX data, which give an excess in the plane region along 0<l<30 deg. compared with -30 deg.<l<0, and which cannot be due to the bulge, spiral arms, a ring, or extinction; 2) new data on the distance of the long bar using the red clump method, together with recent observations of our own that are compared with our model, and that are in agreement with the long-bar scenario.

astro-ph↗
arXiv2004

Evidence for a deficit of young and old stars in the Milky Way inner in-plane disc

We give independent proof of the deficit of stars in the in-plane central disc with respect to the predictions of a pure exponential density distribution. We use three different methods: 1) the inversion of the red clump giant distribution in near-infrared colour-magnitude diagrams to obtain the star density along the line of sight; 2) the determination of the density distribution of 1612 MHz sources by means of the distance determination of OH/IR sources from their kinematical information; 3) an analysis of near and mid-infrared star counts and comparison with models. All the tests give the same result: a defect of stars in the inner disc with respect to an exponential disc (either with constant scaleheight or extrapolated from the outer disc), but only in near plane regions. This deficit might be interpreted as a flare in the vertical distribution. The in-plane density is almost independent of R and not an exponential law. Further away from the plane, however, the density increases towards the centre due to the increase of the scaleheight. Tests also show that this result cannot be due to extinction. The deficit affects both the young and the old populations, so it is probably a rather stable feature of the disc, and might be due to the existence of an in-plane bar sweeping the near-plane stars.

astro-ph↗
arXiv2003

A three-dimensional Galactic extinction model

A large-scale three-dimensional model of Galactic extinction is presented based on the Galactic dust distribution model of Drimmel and Spergel (2001). The extinction A_V to any point within the Galactic disk can be quickly deduced using a set of three-dimensional cartesian grids. Extinctions from the model are compared to empirical extinction measures, including lines-of-sight in and near the Galactic plane using optical and NIR extinction measures; in particular we show how extinction can be derived from NIR color-magnitude diagrams in the Galactic plane to a distance of 8 kiloparsec.

astro-ph↗
arXiv2003

Stellar density distribution in the NIR on the Galactic plane at longitudes 15-27 deg. Clues for the Galactic bar ?

Garzon et al. (1997), Lopez-Corredoira et al. (1999) and Hammersley et al. (2000) have identified in TMGS and DENIS data a large excess of stars at l=27 deg and b=0 deg which might correspond to an in-plane bar. We compared near infrared CAIN star counts and simulations from the Besancon Model of Galaxy on 15 fields between 15 deg and 45 deg in longitude and -2 deg and 2 deg in latitude. Comparisons confirm the existence of an overdensity at longitudes lower than 27 deg which is inhomogeneous and decreases very steeply off the Galactic plane. The observed excess in the star distribution over the predicted density is even higher than 100%. Its distance from the sun is estimated to be lower than 6 kpc. If this overdensity corresponds to the stellar population of the bar, we estimate its half-length to 3.9 +/ -0.4 kpc and its angle from the Sun-center direction to 45 +/- 9 degrees.

astro-ph↗
arXiv2002

Old stellar Galactic disc in near-plane regions according to 2MASS: scales, cut-off, flare and warp

We have pursued two different methods to analyze the old stellar population near the Galactic plane, using data from the 2MASS survey. The first method is based on the isolation of the red clump giant population in the color-magnitude diagrams and the inversion of its star counts to obtain directly the density distribution along the line of sight. The second method fits the parameters of a disc model to the star counts in 820 regions. Results from both independent methods are consistent with each other. The qualitative conclusions are that the disc is well fitted by an exponential distribution in both the galactocentric distance and height. There is not an abrupt cut-off in the stellar disc (at least within R<15 kpc). There is a strong flare (i.e. an increase of scale-height towards the outer Galaxy) which begins well inside the solar circle, and hence there is a decrease of the scale-height towards the inner Galaxy. Another notable feature is the existence of a warp in the old stellar population whose amplitude is coincident with the amplitude of the gas warp. It is shown for low latitude stars (mean height: |z|~300 pc) in the outer disc (galactocentric radius R>6 kpc) that: the scale-height in the solar circle is h_z(R_sun)=3.6e-2 R_sun, the scale-length of the surface density is h_R=0.42 R_sun and the scale-length of the space density in the plane (i.e. including the effect of the flare) is H=0.25 R_sun. The variation of the scale-height due to the flare follows roughly a law h_z(R) =~ h_z(R_sun) exp [(R-R_\odot)/([12-0.6R(kpc)] kpc)] (for R<~15 kpc; R_sun=7.9 kpc). The warp moves the mean position of the disc to a height z_w=1.2e-3 R(kpc)^5.25 sin(phi+(5 deg.)) pc (for R<~13 kpc; R_sun=7.9 kpc).

astro-ph↗