arXiv subjects

F. Navarete

Publications and source records attributed to F. Navarete.

12 recordsLinked to original sources

arXiv2026

Unveiling the enigma of the Nakashima-Deguchi object (IRAS 19312+1950): a candidate Orion KL analog

The Nakashima-Deguchi object (NDO; aka IRAS 19312+1950) has been recognized as an enigmatic object, exhibiting characteristics of both an evolved star and a star-forming region. However, the actual nature of this object remains a topic of ongoing debate. We conducted observations of this object in (sub)millimeter continuum and molecular line emission using the IRAM-30m and APEX telescopes as well as the SMA. Based on SED fitting of single-dish continuum observations, we determined that the cloud hosting NDO has a dust temperature of $25\pm2$ K, a source-averaged (24$^{\prime\prime}$) H$_2$ column density of $(4.4\pm 0.6) \times 10^{22}$ cm$^{-2}$, a dust emissivity index of $1.7\pm0.2$, and a total gas mass of $220\pm21 M_{\odot}$. SMA continuum observations resolve the cloud into at least four dust continuum cores. The centrally peaked core MM1, associated with an SiO maser, is the primary mass reservoir. Single-dish spectroscopic observations of NDO led to the detection of 59 spectral lines attributed to 12 species and their isotopologues. This includes the first detection of deuterated molecules, DCO$^{+}$, DCN, DNC, and HDCO, indicating substantial deuterium abundance. SMA spectroscopic observations detected 75 spectral lines toward MM1, assigned to 12 species and their isotopologues. These lines exhibit diverse morphologies on a scale of $\sim$0.1 pc, likely due to outflow feedback. The observed high-velocity outflow is inconsistent with a spherical morphology and rather resembles a wide-angle bipolar outflow. The presence of deuterated species, and the overall large mass of the complex, the surrounding material of NDO appears more naturally associated with a star-forming environment than with a purely evolved-star scenario. Our investigations led us to postulate that this enigmatic object may represent an Orion KL analog about ten times farther away.

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arXiv2025

Benchmark brown dwarfs -- I. A blue M2 + T5 wide binary and a probable young [M4 + M4] + [T7 + T8] hierarchical quadruple

Benchmark brown dwarfs in wide binary systems are crucial for characterizing substellar objects and calibrating atmospheric and evolutionary models. However, brown dwarf benchmarks with subsolar metallicity, very cool temperatures, or suitability for dynamical mass measurements are rare, limiting our understanding across the full range of mass, age, and metallicity. We present the discovery of two new multiple systems containing T dwarf companions, identified through a targeted search using CatWISE2020 and Gaia catalogues. L 122-88 AB is a wide binary comprising a mildly metal-poor M2 dwarf and a T5 dwarf, separated by 215.6 arcsec at a distance of 33.106+/-0.014 pc. Atmospheric model fitting to the near infrared spectrum of L 122-88 A suggests a mildly metal-poor composition ([Fe/H] = -0.2). UPM J1040-3551 AB is a candidate hierarchical quadruple system at 25.283+/-0.013 pc, consisting of a likely astrometric binary of two M4 dwarfs and a probable unresolved spectral binary of T7 and T8 dwarfs, separated by 65.48 arcsec from the primary. The H-alpha emission detected in UPM J1040-3551 A indicates an age range of 0.3-2.0 Gyr. This age estimate suggests that the T8 component has a mass between 9 and 28 Jupiter masses, potentially classifying it as a planetary-mass object. These systems augment the sample of benchmark brown dwarfs, particularly in the underexplored regime of cool temperature, providing valuable opportunities for refining our understanding of substellar objects.

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arXiv2025

Limits on the Ejecta Mass During the Search for Kilonovae Associated with Neutron Star-Black Hole Mergers: A case study of S230518h, GW230529, S230627c and the Low-Significance Candidate S240422ed

Neutron star-black hole (NSBH) mergers, detectable via their gravitational-wave (GW) emission, are expected to produce kilonovae (KNe). Four NSBH candidates have been identified and followed-up by more than fifty instruments since the start of the fourth GW Observing Run (O4), in May 2023, up to July 2024; however, no confirmed associated KN has been detected. This study evaluates ejecta properties from multi-messenger observations to understand the absence of detectable KN: we use GW public information and joint observations taken from 05.2023 to 07.2024 (LVK, ATLAS, DECam, GECKO, GOTO, GRANDMA, SAGUARO, TESS, WINTER, ZTF). First, our analysis on follow-up observation strategies shows that, on average, more than 50% of the simulated KNe associated with NSBH mergers reach their peak luminosity around one day after merger in the $g,r,i$- bands, which is not necessarily covered for each NSBH GW candidate. We also analyze the trade-off between observation efficiency and the intrinsic properties of the KN emission, to understand the impact on how these constraints affect our ability to detect the KN, and underlying ejecta properties for each GW candidate. In particular, we can only confirm the kilonova was not missed for 1% of the GW230529 and S230627c sky localization region, given the large sky localization error of GW230529 and the large distance for S230627c and, their respective KN faint luminosities. More constraining, for S230518h, we infer the dynamical ejecta and post-merger disk wind ejecta $m_{dyn}, m_{wind}$ $<$ $0.03$ $M_\odot$ and the viewing angle $\theta>25^\circ$. Similarly, the non-astrophysical origin of S240422ed is likely further confirmed by the fact that we would have detected even a faint KN at the time and presumed distance of the S240422ed event candidate, within a minimum 45% credible region of the sky area, that can be larger depending on the KN scenario.

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arXiv2023

Ready for O4 II: GRANDMA Observations of Swift GRBs during eight-weeks of Spring 2022

We present a campaign designed to train the GRANDMA network and its infrastructure to follow up on transient alerts and detect their early afterglows. In preparation for O4 II campaign, we focused on GRB alerts as they are expected to be an electromagnetic counterpart of gravitational-wave events. Our goal was to improve our response to the alerts and start prompt observations as soon as possible to better prepare the GRANDMA network for the fourth observational run of LIGO-Virgo-Kagra (which started at the end of May 2023), and future missions such as SM. To receive, manage and send out observational plans to our partner telescopes we set up dedicated infrastructure and a rota of follow-up adcates were organized to guarantee round-the-clock assistance to our telescope teams. To ensure a great number of observations, we focused on Swift GRBs whose localization errors were generally smaller than the GRANDMA telescopes' field of view. This allowed us to bypass the transient identification process and focus on the reaction time and efficiency of the network. During 'Ready for O4 II', 11 Swift/INTEGRAL GRB triggers were selected, nine fields had been observed, and three afterglows were detected (GRB 220403B, GRB 220427A, GRB 220514A), with 17 GRANDMA telescopes and 17 amateur astronomers from the citizen science project Kilonova-Catcher. Here we highlight the GRB 220427A analysis where our long-term follow-up of the host galaxy allowed us to obtain a photometric redshift of $z=0.82\pm0.09$, its lightcurve elution, fit the decay slope of the afterglows, and study the properties of the host galaxy.

astro-ph.HE↗

arXiv2023

Multi-band analyses of the bright GRB 230812B and the associated SN2023pel

GRB~230812B is a bright and relatively nearby ($z =0.36$) long gamma-ray burst (GRB) that has generated significant interest in the community and has thus been observed over the entire electromagnetic spectrum. We report over 80 observations in X-ray, ultraviolet, optical, infrared, and sub-millimeter bands from the GRANDMA (Global Rapid Advanced Network for Multi-messenger Addicts) network of observatories and from observational partners. Adding complementary data from the literature, we then derive essential physical parameters associated with the ejecta and external properties (i.e. the geometry and environment) of the GRB and compare with other analyses of this event. We spectroscopically confirm the presence of an associated supernova, SN2023pel, and we derive a photospheric expansion velocity of v $\sim$ 17$\times10^3$ km s$^{-1}$. We analyze the photometric data first using empirical fits of the flux and then with full Bayesian Inference. We again strongly establish the presence of a supernova in the data, with a maximum (pseudo-)bolometric luminosity of $5.75 \times 10^{42}$ erg/s, at $15.76^{+0.81}_{-1.21}$ days (in the observer frame) after the trigger, with a half-max time width of 22.0 days. We compare these values with those of SN1998bw, SN2006aj, and SN2013dx. Our best-fit model favours a very low density environment ($\log_{10}({n_{\rm ISM}/{\rm cm}^{-3}}) = -2.38^{+1.45}_{-1.60}$) and small values for the jet's core angle $\theta_{\rm core} = 1.54^{+1.02}_{-0.81} \ \rm{deg}$ and viewing angle $\theta_{\rm obs} = 0.76^{+1.29}_{-0.76} \ \rm{deg}$. GRB 230812B is thus one of the best observed afterglows with a distinctive supernova bump.

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arXiv2022

The long-term spectral changes of eta Carinae: are they caused by a dissipating occulter as indicated by CMFGEN models?

Eta Carinae ($\eta$\,Car) exhibits a unique set of P Cygni profiles with both broad and narrow components. Over many decades, the spectrum has changed -- there has been an increase in observed continuum fluxes and a decrease in FeII and HI emission line equivalent widths. The spectrum is evolving towards that of a P Cygni star such as P~Cygni itself and HDE~316285. The spectral evolution has been attributed to intrinsic variations such as a decrease in the mass-loss rate of the primary star or differential evolution in a latitudinal-dependent stellar wind. However intrinsic wind changes conflict with three observational results: the steady long-term bolometric luminosity; the repeating X-ray light curve over the binary period; and the constancy of the dust-scattered spectrum from the Homunculus. We extend previous work that showed a secular strengthening of P~Cygni absorptions by adding more orbital cycles to overcome temporary instabilities and by examining more atomic transitions. {\sc cmfgen} modeling of the primary wind shows that a time-decreasing mass-loss rate is not the best explanation for the observations. However, models with a `small' dissipating absorber in our line-of-site can explain both the increase in brightness and changes in the emission and P Cygni absorption profiles. If the spectral evolution is caused by the dissipating circumstellar medium, and not by intrinsic changes in the binary, the dynamical timescale to recover from the Great Eruption is much less than a century, different from previous suggestions.

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arXiv2022

The GRANDMA network in preparation for the fourth gravitational-wave observing run

GRANDMA is a world-wide collaboration with the primary scientific goal of studying gravitational-wave sources, discovering their electromagnetic counterparts and characterizing their emission. GRANDMA involves astronomers, astrophysicists, gravitational-wave physicists, and theorists. GRANDMA is now a truly global network of telescopes, with (so far) 30 telescopes in both hemispheres. It incorporates a citizen science programme (Kilonova-Catcher) which constitutes an opportunity to spread the interest in time-domain astronomy. The telescope network is an heterogeneous set of already-existing observing facilities that operate coordinated as a single observatory. Within the network there are wide-field imagers that can observe large areas of the sky to search for optical counterparts, narrow-field instruments that do targeted searches within a predefined list of host-galaxy candidates, and larger telescopes that are devoted to characterization and follow-up of the identified counterparts. Here we present an overview of GRANDMA after the third observing run of the LIGO/VIRGO gravitational-wave observatories in $2019-2020$ and its ongoing preparation for the forthcoming fourth observational campaign (O4). Additionally, we review the potential of GRANDMA for the discovery and follow-up of other types of astronomical transients.

astro-ph.IM↗

arXiv2022

GRANDMA Observations of ZTF/Fink Transients during Summer 2021

We present our follow-up observations with GRANDMA of transient sources revealed by the Zwicky Transient Facility (ZTF). Over a period of six months, all ZTF triggers were examined in real time by a dedicated science module implemented in the Fink broker, which will be used for the data processing of the Vera C. Rubin Observatory. In this article, we present three selection methods to identify kilonova candidates. Out of more than 35 million candidates, a hundred sources have passed our selection criteria. Six were then followed-up by GRANDMA (by both professional and amateur astronomers). The majority were finally classified either as asteroids or as supernovae events. We mobilized 37 telescopes, bringing together a large sample of images, taken under various conditions and quality. To complement the orphan kilonova candidates (those without associated gamma-ray bursts, which were all), we included three additional supernovae alerts to conduct further observations of during summer 2021. We demonstrate the importance of the amateur astronomer community that contributed images for scientific analyzes of new sources discovered in a magnitude range r'=17-19 mag. We based our rapid kilonova classification on the decay rate of the optical source that should exceed 0.3 mag/day. GRANDMA's follow-up determined the fading rate within 1.5+/-1.2 days post-discovery, without waiting for further observations from ZTF. No confirmed kilonovae were discovered during our observing campaign. This work will be continued in the coming months in the view of preparing for kilonova searches in the next gravitational-wave observing run O4.

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arXiv2021

Spectroscopic Signatures of the Vanishing Natural Coronagraph of eta Carinae

Eta Carinae is a massive interacting binary system shrouded in a complex circumstellar environment whose evolution is the source of the long-term brightening observed during the last 80 years. An occulter, acting as a natural coronagraph, impacts observations from our perspective, but not from most other directions. Other sight-lines are visible to us through studies of the Homunculus reflection nebula. The coronagraph appears to be vanishing, decreasing the extinction towards the central star, and causing the star's secular brightening. In contrast, the Homunculus remains at an almost constant brightness. The coronagraph primarily suppresses the stellar continuum, to a lesser extent the wind lines, and not the circumstellar emission lines. This explains why the absolute values of equivalent widths (EWs) of the emission lines in our direct view are larger than those seen in reflected by the Homunculus, why the direct view absolute EWs are decreasing with time, and why lower-excitation spectral wind lines formed at larger radii (e.g. FeII 4585A) decrease in intensity at a faster pace than higher excitation lines that form closer to the star (e.g. H\delta). Our main result is that the star, despite its 10-fold brightening over two decades, is relatively stable. A vanishing coronagraph that can explain both the large flux evolution and the much weaker spectral evolution. This is contrary to suggestions that the long-term variability is intrinsic to the primary star that is still recovering from the Great Eruption with a decreasing mass-loss rate and a polar wind that is evolving at a slower pace than at the equator.

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arXiv2020

Searching for active low-mass stars in CMa star-forming region: multi-band photometry with T80S

An exotic environment surrounds the young stellar groups associated with the Canis Major (CMa) OB1/R1 region, which probably was formed under feedback from at least three supernova events having occurred a few million years ago. We use astrometric data from the Gaia-DR2 to confirm the membership of the stars in CMa R1, based on proper motion and parallax, which revealed 514 new members and candidates. The mean age of 5 Myr estimated from the color-magnitude diagram characterizes the sources as likely pre-main sequence candidates. In total, a sample of 694 stars detected with the T80-South telescope was analyzed according to different color-color diagrams, which were compared with theoretical colors from evolutionary models, aiming to reveal the objects that exhibit color excess due to accretion processes. Accretion and magnetic activity were also explored on the basis of empirical flux-flux relation, such as F660 and F861 that are related to Halpha and Ca II triplet emission, respectively. A low fraction (3 percent) of the sample have Halpha excess and other colors expected for stars exhibiting chromospheric activity. The number of Class I and Class II objects, identified by the infrared (WISE) colors, indicates a disk fraction of 6 percent, which is lower than the expected for stellar clusters with similar age. A such large sample of objects associated with CMa R1 without evidences of circumstellar accretion can be interpreted as a lack of disk-bearing stars, unusual for young star-forming regions. However, this may be explained as the result of supernova events.

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arXiv2016

He II $\lambda$4686 emission from the massive binary system in $\eta$ Car: constraints to the orbital elements and the nature of the periodic minima

{\eta} Carinae is an extremely massive binary system in which rapid spectrum variations occur near periastron. Most notably, near periastron the He II $\lambda 4686$ line increases rapidly in strength, drops to a minimum value, then increases briefly before fading away. To understand this behavior, we conducted an intense spectroscopic monitoring of the He II $\lambda 4686$ emission line across the 2014.6 periastron passage using ground- and space-based telescopes. Comparison with previous data confirmed the overall repeatability of EW(He II $\lambda 4686$), the line radial velocities, and the timing of the minimum, though the strongest peak was systematically larger in 2014 than in 2009 by 26%. The EW(He II $\lambda 4686$) variations, combined with other measurements, yield an orbital period $2022.7\pm0.3$ d. The observed variability of the EW(He II $\lambda 4686$) was reproduced by a model in which the line flux primarily arises at the apex of the wind-wind collision and scales inversely with the square of the stellar separation, if we account for the excess emission as the companion star plunges into the hot inner layers of the primary's atmosphere, and including absorption from the disturbed primary wind between the source and the observer. This model constrains the orbital inclination to $135^\circ$-$153^\circ$, and the longitude of periastron to $234^\circ$-$252^\circ$. It also suggests that periastron passage occurred on $T_0 = 2456874.4\pm1.3$ d. Our model also reproduced EW(He II $\lambda 4686$) variations from a polar view of the primary star as determined from the observed He II $\lambda 4686$ emission scattered off the Homunculus nebula.

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arXiv2011

The Stellar Content of Obscured Galactic Giant HII Regions. VII. W3

Spectrophotometric distances in the K band have been reported by different authors for a number of obscured Galactic HII regions. Almost 50% of them show large discrepancies compared to the classical method using radial velocities measured in the radio spectral region. In order to provide a crucial test of both methods, we selected a target which does not present particular difficulty for any method and which has been measured by as many techniques as possible. The W3 star forming complex, located in the Perseus arm, offers a splendid opportunity for such a task. We used the NIFS spectrograph on the Frederick C. Gillett Gemini North telescope to classify candidate "naked photosphere" OB stars based on 2MASS photometry. Two of the targets are revealed to be mid O-type main sequence stars leading to a distance of d = 2.20 kpc. This is in excellent agreement with the spectrophotometric distance derived in the optical band (d = 2.18 kpc, Humphreys 1978) and with a measurement of the W3 trigonometric parallax (d = 1.95 kpc, Xu et al. 2006). Such results confirm that the spectrophotometric distances in the K band are reliable. The radio derived kinematic distance, on the contrary, gives a distance twice as large (d = 4.2 kpc, Russeil 2003). This indicates that this region of Perseus arm does not follow the Galactic rotation curve, and this may be the case also for other HII regions for which discrepancies have been found.

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