arXiv subjects

A. Luna

Publications and source records attributed to A. Luna.

At least 19 recordsLinked to original sources

arXiv2026

Unresolved triple systems in the aged open cluster Trumpler 19: Discovery, confirmation, and implications

It is difficult to identify unresolved triple and higher-order systems beyond the solar vicinity. Star clusters yield controlled environments with known physical parameters, providing a way to explore homogeneous stellar samples. Combining modern optical and near-IR surveys, our main goal is to explore the region of the color-magnitude diagrams located above the sequence of equal-mass binaries, which is inhabited by unresolved triple and quadruple systems. Specifically, here we aim to discover and characterize the presence of multiple systems in the aged open star cluster Trumpler 19. We selected cluster members using Gaia astrometry and photometry from the VVVX and DECAPS2 surveys. We made optical and near-IR color-magnitude diagrams to select stars located >0.75 mag above the cluster main sequence, including suitable unresolved triple and quadruple systems. We confirm previous results that there is a sizable sequence of unresolved binaries in Trumpler 19. We also report the discovery of a sequence of unresolved multiple systems in this cluster, and confirm some of these multiple systems via radial velocities measured by the ESO KMOS VVVX-GalCen spectroscopic survey. The fraction of multiple stars in this cluster is comparable to that of the solar neighborhood, with the caveat that the local sample probes deeper down the main sequence. The fraction of unresolved triples and quadruples is also three times higher than that of the open cluster M 67, which is of a similar age and chemical composition. The discovery of unresolved triple systems in Trumpler 19 leads to our main conclusion that these systems were able to survive within the cluster for nearly 4 Gyr. In addition, this cluster contains more multiple systems than M 67, which has a similar total present mass. Further investigations are needed to unveil if this is a primordial feature or the result of dynamical evolution.

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arXiv2026

Extinction law and stellar mass in the Nuclear Bulge from kinematically-selected red clump stars

The Nuclear Bulge of the Milky Way harbors stellar populations that provide crucial insights into galaxy formation processes and serve as a nearby analog for understanding bulge formation in external galaxies. However, detailed studies of this region are severely hampered by extreme and highly variable interstellar extinction, which obscures the intrinsic stellar properties and impedes accurate stellar mass determinations. Our goal is to measure the extinction law towards the Nuclear Bulge and to estimate its stellar density. We developed a method to determine the extinction law towards the Nuclear Bulge by kinematically selecting red clump stars belonging to this region. We created a high-spatial resolution reddening map, and computed stellar mass with completeness-corrected red clump star counts, scaled from empirical measurements. We find a total-to-selective extinction ratio of $\mathrm{A_K/{E_{H-K}} = 1.259 \pm 0.074}$, and an extinction ratio of $\mathrm{A_H/A_K = 1.794 \pm 0.046}$, which are consistent with previous works. The high-spatial resolution reddening map shows clear filamentary structures, and a gradient in the extinction over the giant molecular cloud G0.253+0.016 (i.e., the Brick). From the star counts, we measured a stellar mass of $\mathrm{12.2~\pm2.6\times10^8~M_{\odot}}$ for the Nuclear Bulge, in agreement with other mass estimates.

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arXiv2024

The VISTA Variables in the V\'ia L\'actea eXtended (VVVX) ESO public survey: Completion of the observations and legacy

The ESO public survey VISTA Variables in the V\'ia L\'actea (VVV) surveyed the inner Galactic bulge and the adjacent southern Galactic disk from $2009-2015$. Upon its conclusion, the complementary VVV eXtended (VVVX) survey has expanded both the temporal as well as spatial coverage of the original VVV area, widening it from $562$ to $1700$ sq. deg., as well as providing additional epochs in $JHK_{\rm s}$ filters from $2016-2023$. With the completion of VVVX observations during the first semester of 2023, we present here the observing strategy, a description of data quality and access, and the legacy of VVVX. VVVX took $\sim 2000$ hours, covering about 4% of the sky in the bulge and southern disk. VVVX covered most of the gaps left between the VVV and the VISTA Hemisphere Survey (VHS) areas and extended the VVV time baseline in the obscured regions affected by high extinction and hence hidden from optical observations. VVVX provides a deep $JHK_{\rm s}$ catalogue of $\gtrsim 1.5\times10^9$ point sources, as well as a $K_{\rm s}$ band catalogue of $\sim 10^7$ variable sources. Within the existing VVV area, we produced a $5D$ map of the surveyed region by combining positions, distances, and proper motions of well-understood distance indicators such as red clump stars, RR Lyrae, and Cepheid variables. In March 2023 we successfully finished the VVVX survey observations that started in 2016, an accomplishment for ESO Paranal Observatory upon 4200 hours of observations for VVV+VVVX. The VVV+VVVX catalogues complement those from the Gaia mission at low Galactic latitudes and provide spectroscopic targets for the forthcoming ESO high-multiplex spectrographs MOONS and 4MOST.

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arXiv2024

New candidate hypervelocity red clump stars in the inner Galactic bulge

We search for high-velocity stars in the inner region of the Galactic bulge using a selected sample of red clump stars. Some of those stars might be considered hypervelocity stars (HVSs). Even though the HVSs ejection relies on an interaction with the supermassive black hole (SMBH) at the centre of the Galaxy, there are no confirmed detections of HVSs in the inner region of our Galaxy. With the detection of HVSs, ejection mechanism models can be constrained by exploring the stellar dynamics in the Galactic centre through a recent stellar interaction with the SMBH. Based on a previously developed methodology by our group, we searched with a sample of preliminary data from version 2 of the Vista Variables in the Via Lactea (VVV) Infrared Astrometric Catalogue (VIRAC2) and Gaia DR3 data, including accurate optical and NIR proper motions. This search resulted in a sample of 46 stars with transverse velocities larger than the local escape velocity within the Galactic bulge, of which 4 are prime candidate HVSs with high-proper motions consistent with being ejections from the Galactic centre. Adding to that, we studied a sample of reddened stars without a Gaia DR3 counterpart and found 481 stars with transverse velocities larger than the local escape velocity, from which 65 stars have proper motions pointing out of the Galactic centre and are candidate HVSs. In total, we found 69 candidate HVSs pointing away from the Galactic centre with transverse velocities larger than the local escape velocity.

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arXiv2023

Variable stars in the field of the Galactic bulge globular cluster NGC 6522

We present a comprehensive analysis of the variable stars projected on the field of the Galactic bulge globular cluster NGC 6522, offering valuable insights into their characteristics. Using proper motions from Gaia DR3, we aim to distinguish between field stars and true cluster members. For an accurate color-magnitude diagram of the member stars, we produced a differential reddening map. We detect and discuss the peculiarities of variable stars of the types RR Lyrae, type II Cepheids, Long Period Variables (LPV) and eclipsing binaries, whose light curves are available through the OGLE III and IV databases. Notably, we explore the variable V24, which shows a prominent phase modulation resulting from period changes in a time scale of ~1100 days. The variable stars among the cluster members serve as indicators of the cluster metallicity and distance; these determinations are based on their light curves. With the Fourier light curve decomposition of three RRc stars, we have derived the following cluster parameters: the metallicity in the spectroscopic scale [Fe/H]$_{\rm UVES}$=--1.16 $\pm$0.09; and the mean distance $D=8.77 \pm 0.16$ kpc.

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arXiv2023

The variable stars in the field of NGC 6139: A critical approach to their reddening and membership

We present a CCD $VI$ time-series analysis of the globular cluster NGC 6139 and its variable star population. Using the astrometric data available in $Gaia$-DR3 we performed a membership analysis that enabled the construction of a clean Colour-Magnitude Diagram (CMD). Variable stars in the field of the cluster reported by $Gaia$-DR3 and newly discovered ones in this paper are classified and their membership is critically evaluated. We report two cluster member RRc (V12, V15) and four SR (V13, V14, V17, V18) not previously detected and assign variable names to V11 and V16 detected by $Gaia$ as they proof to be cluster members. Light curves and periods for non-member $Gaia$ eclipsing binaries, semi regular variables and newly detected RR Lyrae stars are provided. Fourier decomposition of the light curves of the cluster member RRab and RRc stars leads to the values [Fe/H]=$-1.63$ dex, and distance of 9.63$\pm$0.68 kpc. The Oosterhoff type II nature of the cluster is confirmed. We adopted the mean reddening $E(B-V)$=0.786 mag and performed a differential reddening analysis based on the dispersion of the red giant branch. The differential map allowed a mild correction of the CMD.

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arXiv2023

The stellar population responsible for a kiloparsec size superbubble seen in the JWST "phantom" images of NGC628

We here study the multi-band properties of a kiloparsec-size superbubble in the late-type spiral galaxy NGC628. The superbubble is the largest of many holes seen in the early release images using JWST/MIRI filters that trace the Polycyclic Aromatic Hydrocarbon (PAH) emissions. The superbubble is located in the interarm region ~3 kpc from the galactic center in the south-east direction. The shell surrounding the superbubble is detected in HI, CO, and Halpha with an expansion velocity of 12 km/s, and contains as much as 2x10^7 Msun of mass in gas that is mostly in molecular form. We find a clear excess of blue, bright stars inside the bubble as compared to the surrounding disk on the HST/ACS images. These excess blue, bright stars are part of a stellar population of 10^5 Msun mass that is formed over the last 50 Myr in different star formation episodes, as determined from an analysis of color-magnitude diagrams using a Bayesian technique. The mechanical power injected by the massive stars of these populations is sufficient to provide the energy necessary for the expansion of the shell gas. Slow and steady, rather than violent, injection of energy is probably the reason for the maintenance of the shell structure over the kiloparsec scale. The expanding shell is currently the site for triggered star formation as inferred from the JWST 21 micron (F2100W filter) and the Halpha images.

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arXiv2023

Near-Infrared Polarimetry and H$_2$ emission toward Massive Young Stars: Discovery of a Bipolar Outflow associated to S235 e2s3

We present a near-infrared $H$ band polarimetric study toward the S235 e2s3 protostar, obtained using the POLICAN instrument on the 2.1m OAGH telescope. The images reveal a bipolar outflow with a total length of about 0.5pc. The outflow nebulosity presents a high degree of linear polarization ($\sim80\%$) and reveals a centrosymmetric pattern with the polarization position angles. The polarization characteristics suggest their origin to be single scattering associated with dust in the outflow. Using multiwavelength archival data, we performed spectral energy distribution (SED) fitting based on radiative transfer models of turbulent core accretion theory. The best-fit SED model indicated that the protostar has a mass of $6.8\pm1.2\,M_\odot$, with a disk accretion rate of $3.6\pm1.2\times10^{-4}\,M_\odot\,yr^{-1}$ and a total bolometric luminosity of $9.63\pm2.1\times10^{3}\,L_\odot$. Narrowband H$_2$ ($2.12\,\mu$m) observations show shocked emission along the bipolar lobes tracing the jet's interaction with the surrounding medium. The estimated H$_2$ luminosity of the outflow is $2.3_{-1.3}^{+3.5}\,L_\odot$, which matched the known power-law correlation with the source bolometric luminosity, similar to other high-mass outflows. The orientation of the bipolar outflow was found to be parallel to the local magnetic field direction. The overall results assert the fact that the S235 e2s3 source is a massive young star driving a highly collimated bipolar outflow through disk accretion.

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arXiv2021

Magnetic fields and Star Formation around HII regions: The S235 complex

Magnetic fields are ubiquitous and essential in star formation. In particular, their role in regulating formation of stars across diverse environments like HII regions needs to be well understood. In this study, we present magnetic field properties towards the S235 complex using near-infrared (NIR) $H$-band polarimetric observations, obtained with the Mimir and POLICAN instruments. We selected 375 background stars in the field through combination of Gaia distances and extinctions from NIR colors. The plane-of-sky (POS) magnetic field orientations inferred from starlight polarization angles reveal a curved morphology tracing the spherical shell of the HII region. The large-scale magnetic field traced by Planck is parallel to the Galactic plane. We identified 11 dense clumps using $1.1\,\mathrm{mm}$ dust emission, with masses between $33-525\,\rm M_\odot$. The clump averaged POS magnetic field strengths were estimated to be between $36-121\,\mathrm{μG}$, with a mean of ${\sim}65\,\mathrm{μG}$. The mass-to-flux ratios for the clumps are found to be sub-critical with turbulent Alfvén Mach numbers less than 1, indicating a strongly magnetized region. The clumps show scaling of magnetic field strength vs density with a power-law index of $0.52\pm0.07$, similar to ambipolar diffusion models. Our results indicate the S235 complex is a region where stellar feedback triggers new stars and the magnetic fields regulate the rate of new star formation.

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arXiv2020

Infrared Dark Clouds and high-mass star formation activity in Galactic Molecular Clouds

Ever since their discovery, Infrared dark clouds (IRDCs) are generally considered to be the sites just at the onset of high-mass (HM) star formation. In recent years, it has been realized that not all IRDCs harbour HM Young Stellar Objects (YSOs). Only those IRDCs satisfying a certain mass-size criterion, or equivalently above a certain threshold density, are found to contain HMYSOs. In all cases, IRDCs provide ideal conditions for the formation of stellar clusters. In this paper, we study the massive stellar content of IRDCs to re-address the relation between IRDCs and HM star formation. For this purpose, we have identified all IRDCs associated to a sample of 12 Galactic molecular clouds (MCs). The selected MCs have been the target of a systematic search for YSOs in an earlier study. The catalogued positions of YSOs have been used to search all YSOs embedded in each identified IRDC. In total, we have found 834 YSOs in 128 IRDCs. The sample of IRDCs have mean surface densities of 319 Mo/pc2, mean mass of 1062 Mo, and a mass function power-law slope -1.8, which are similar to the corresponding properties for the full sample of IRDCs and resulting physical properties in previous studies. We find that all those IRDCs containing at least one intermediate to high-mass young star satisfy the often-used mass-size criterion for forming HM stars. However, not all IRDCs satisfying the mass-size criterion contain HM stars. We find that the often used mass-size criterion corresponds to 35% probability of an IRDC forming a massive star. Twenty five (20%) of the IRDCs are potential sites of stellar clusters of mass more than 100 Mo.

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arXiv2020

The Near-Infrared Polarization of the Pre-Planetary Nebula Frosty Leo

We present a near-infrared imaging polarimetric study of the pre-planetary nebula: Frosty Leo. The observations were carried out in J, H and K' bands using the new polarimeter POLICAN mounted on the 2.1m telescope of the Guillermo Haro Astrophysical Observatory, Sonora, Mexico. The most prominent result observed in the polarization maps is a large and well defined dusty envelope (35\arcsec\ diameter in H-band). The polarization position angles in the envelope are particularly well ordered and nearly parallel to the equator of the nebula (seen in J and H bands). The nebula presents a known bipolar outflow and the envelope completely wraps around it. Within the bipolar lobes, we find high polarization levels ranging from $60\%$ (J band) to $90\%$ (K' band) and the polarization angles trace a centrosymmetric pattern. We found the remnants of superwind shells at the edges of the bipolar lobes and the duration of this phase is around 600 yrs. The origin of polarization features in the nebula is most likely due to a combination of single and multiple scattering. Our results clearly demonstrate new structures that provide new hints on the evolution of Frosty Leo from its previous asymptotic giant branch phase.

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arXiv2019

Dynamics of cluster-forming hub-filament systems: The case of the high-mass star-forming complex Monoceros R2

High-mass stars and star clusters commonly form within hub-filament systems. Monoceros R2, harbors one of the closest such systems, making it an excellent target for case studies. We investigate the morphology, stability and dynamical properties of the hub-filament system on basis of 13CO and C18O observations obtained with the IRAM-30m telescope and H2 column density maps derived from Herschel dust emission observations. We identified the filamentary network and characterized the individual filaments as either main (converging into the hub) or secondary (converging to a main filament) filaments. The main filaments have line masses of 30-100 Msun/pc and show signs of fragmentation. The secondary filaments have line masses of 12-60 Msun/pc and show fragmentation only sporadically. In the context of Ostriker's hydrostatic filament model, the main filaments are thermally super-critical. If non-thermal motions are included, most of them are trans-critical. Most of the secondary filaments are roughly trans-critical regardless of whether non-thermal motions are included or not. From the main filaments, we estimate a mass accretion rate of 10(-4)-10(-3) Msun/pc into the hub. The secondary filaments accrete into the main filaments with a rate of 0.1-0.4x10(-4) Msun/pc. The main filaments extend into the hub. Their velocity gradients increase towards the hub, suggesting acceleration of the gas. We estimate that with the observed infall velocity, the mass-doubling time of the hub is ~2.5 Myr, ten times larger than the free-fall time, suggesting a dynamically old region. These timescales are comparable with the chemical age of the HII region. Inside the hub, the main filaments show a ring- or a spiral-like morphology that exhibits rotation and infall motions. One possible explanation for the morphology is that gas is falling into the central cluster following a spiral-like pattern.

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arXiv2018

Early science with the Large Millimetre Telescope: An LMT/AzTEC 1.1 mm Survey of Dense Cores in the Monoceros R2 Giant Molecular Cloud

We present a 1.1~mm census of dense cores in the Mon~R2 Giant Molecular Cloud with the AzTEC instrument on the Large Millimeter Telescope (LMT). We detect 295 cores (209 starless, and 86 with protostars) in a two square degree shallow survey. We also carry out a deep follow-up survey of 9 regions with low to intermediate ($3 $10~$M_{\odot}$ are exclusively found in regions with high core number densities and that the CMF of the starless cores has an excess of low-mass cores ($<$5~$M_{\odot}$) compared to the CMF of protostellar cores. We report a power law correlation of index $1.99 \pm 0.03$ between local core mass density and gas column density (as traced by Herschel) over a wide range of size scales (0.3-5~pc). This power law is consistent with that predicted for thermal fragmentation of a self-gravitating sheet.

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arXiv2018

Filamentary Structures and Star Formation Activities in the Sites S234, V582, and IRAS 05231+3512

To investigate the physical processes, we present observational results of the sites S234, V582, and IRAS 05231+3512 situated toward l = 171.7 - 174.1 degrees. Based on the CO line data, we find that these sites are not physically connected, and contain at least one filament (with length > 7 pc). The observed line masses (M_line,obs) of the filaments associated with V582 and IRAS 05231+3512 are ~37 and ~28 M_sun/pc, respectively. These filaments are characterized as thermally supercritical, and harbor several clumps. Groups of infrared-excess sources and massive B-type stars are observed toward the filament containing V582, while a very little star formation (SF) activity is found around IRAS 05231+3512. Our results favour radial collapse scenario in the filaments harboring V582 and IRAS 05231+3512. In the site S234, two filaments (i.e. ns1 (M_line,obs ~130 M_sun/pc) and ns2 (M_line,obs ~45 M_sun/pc)) are identified as thermally supercritical. An extended temperature structure at 27-30 K surrounds a relatively cold (~19 K) ~8.9 pc long filament ns1. At least four condensations (M_clump ~70-300 M_sun) are seen in ns1, and are devoid of the GMRT 610 MHz radio emission. The filament ns2 hosting clumps is devoid of ongoing SF, and could be at an early stage of fragmentation. An intense SF activity, having the SF efficiency ~3.3% and SF rate ~40-20 M_sun/Myr (for t_sf ~1-2 Myr), is observed in ns1. The feedback of massive stars in S234 seems to explain the observed SF in the filament ns1.

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arXiv2018

Characterization and Performance of the Cananea Near-infrared Camera (CANICA)

We present details of characterization and imaging performance of the Cananea Near-infrared camera (CANICA) at the 2.1m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, Mexico. CANICA has a HAWAII array with a HgCdTe detector of 1024 x 1024 pixels covering a field of view of 5.5 x 5.5 arcmin^2 with a plate scale of 0.32 arcsec/pixel. The camera characterization involved measuring key detector parameters: conversion gain, dark current, readout noise, and linearity. The pixels in the detector have a full-well-depth of 100,000 e- with the conversion gain measured to be 5.8 e-/ADU. The time-dependent dark current was estimated to be 1.2 e-/sec. Readout noise for correlated double sampled (CDS) technique was measured to be 30 e-/pixel. The detector shows 10% non-linearity close to the full-well-depth. The non-linearity was corrected within 1% levels for the CDS images. Full-field imaging performance was evaluated by measuring the point spread function, zeropoints, throughput, and limiting magnitude. The average zeropoint value in each filter are J = 20.52, H = 20.63, and K = 20.23. The saturation limit of the detector is about sixth magnitude in all the primary broadbands. CANICA on the 2.1m OAGH telescope reaches background-limited magnitudes of J = 18.5, H = 17.6, and K = 16.0 for a signal-to-noise ratio of 10 with an integration time of 900s.

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arXiv2018

POLICAN: A Near-infrared Imaging Polarimeter at the 2.1m OAGH Telescope

POLICAN is a near-infrared imaging linear polarimeter developed for the Cananea Near-infrared Camera (CANICA) at the 2.1m telescope of the Guillermo Haro Astrophysical Observatory (OAGH) located in Cananea, Sonora, Mexico. POLICAN is mounted ahead of CANICA and consist of a rotating super-achromatic 1-2.7 micron half-wave plate (HWP) as the modulator and a fixed wire-grid polarizer as the analyzer. CANICA has a 1024 x 1024 HgCdTe detector with a plate scale of 0.32 arcsec/pixel and provides a field of view of 5.5 x 5.5 arcmin^2. The polarimetric observations are carried out by modulating the incoming light through different steps of half-wave plate angles 0, 22.5, 45, 67.5 deg, to establish linear Stokes parameters (I, Q, and U). Image reduction consists of dark subtraction, polarimetric flat fielding, and sky subtraction. The astrometry and photometric calibrations are performed using the publicly available data from the Two Micron All Sky Survey. Polarimetric calibration includes observations of globular clusters and polarization standards available in the literature. Analysis of multiple observations of globular clusters yielded an instrumental polarization of 0.51%. Uncertainties in polarization range from 0.1% to 10% from the brightest 7 mag to faintest 16 mag stars. The polarimetric accuracy achieved is better than 0.5% and the position angle errors less than 5 deg for stars brighter than 13 mag in H-band. POLICAN is mainly being used to study the scattered polarization and magnetic fields in and around star-forming regions of the interstellar medium.

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arXiv2018

Period changes in the RR Lyrae stars of NGC 6171 (M107)

Based on photometric data obtained between 1935 and 2017, $O-C$ diagrams were built for 22 RR Lyrae stars in the globular cluster NGC 6171, leading to the discovery of secular period changes in 4 variables for which we have calculated their period change rates $β$. In contrast we find that $82\%$ of the sample stars have stable periods over the last 82 years. For the stable period stars, the whole data base has been employed to refine their periods. Among the period changing stars, three (V10, V12 and V16) have decreasing periods larger than expected from stellar evolution. Despite these individual cases of significant period change rate, the golbal average of the measured period changes in the cluster is basically zero, in consonance with theoretical predictions for clusters with redder horizontal branches. The hitherto unpublished observations, now brought into public domain, are employed to calculate a set of times of maximum light which are used in the present analysis.

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arXiv2017

Early Science with the Large Millimetre Telescope: Fragmentation of molecular clumps in the Galaxy

Sensitive, imaging observations of the 1.1 mm dust continuum emission from a 1 deg^2 area collected with the AzTEC bolometer camera on the Large Millimeter Telescope are presented. A catalog of 1545 compact sources is constructed based on a Wiener-optimization filter. These sources are linked to larger clump structures identified in the Bolocam Galactic Plane Survey. Hydrogen column densities are calculated for all sources and mass and mean volume densities are derived for the subset of sources for which kinematic distances can be assigned. The AzTEC sources are localized, high density peaks within the massive clumps of molecular clouds and comprise 5-15% of the clump mass. We examine the role of the gravitational instability in generating these fragments by comparing the mass of embedded AzTEC sources to the Jeans' mass of the parent BGPS object. For sources with distances less than 6 kpc the fragment masses are comparable to the clump Jeans' mass, despite having isothermal Mach numbers between 1.6 and 7.2. AzTEC sources linked to ultra-compact HII regions have mass surface densities greater than the critical value implied by the mass-size relationship of infrared dark clouds with high mass star formation while AzTEC sources associated with Class II methanol masers have mass surface densities greater than 0.7 g cm^{-2} that approaches the proposed threshold required to form massive stars.

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