arXiv subjects

Carlos Contreras Peña

Publications and source records attributed to Carlos Contreras Peña.

18 recordsLinked to original sources

arXiv2026

SPICY 30021: an embedded bona fide FUor with a mid-infrared precursor

Unstable mass accretion in young stellar objects (YSOs) often leads to observable outbursts, which play a key role in stellar mass assembly during pre-main-sequence evolution. The highest-amplitude, longest-duration events are classified as FUors. Until recently, only 50 FUor events had been confirmed. Many occur in embedded protostars, which are difficult to monitor in optical surveys. We present photometric and spectroscopic observations of SPICY 30021, an eruptive young star discovered in the mid-infrared (MIR) NEOWISE time series. We aim to construct its spectral energy distribution and characterise its eruptive nature. We compiled multi-wavelength photometric time series from NEOWISE, VVV and VVV-RENEW, and obtained photometric and spectroscopic observations during the outburst with SOAR, Magellan and VLT, including data from the ESO public survey VVVX-GalCen. We identified the outbursting source, separated it from nearby companions, and estimated the line-of-sight extinction from spectroscopic features. Stellar parameters were constrained using radial velocity, proper motions and stellar evolution models. SPICY 30021 is an optically obscured FUor with a total interstellar and circumstellar extinction of Av = 12.5 mag. Its spectrum closely resembles those of classical FUors. Multiple methods yield a distance of 1.7+_0.4 kpc. Its accretion luminosity is Lacc = 32 L_sol, moderate among FUors. Quiescent near-infrared photometry is consistent with a young 0.9 M_sol progenitor, although the mass depends on the adopted model and distance. We confirm SPICY 30021 as a bona fide FUor event. Its MIR precursor suggests an outside-in triggering mechanism.

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arXiv2026

The long-term outburst(s) of GPSV16: from an intermediate to a FUor classification

FU Ori outbursts are thought to play a key role in stellar mass assembly and in the chemistry of protoplanetary disks during the early formation of stars. However, uncertainties remain regarding the universality of these events and the physical mechanism driving the high-amplitude variability. In this work, we present an analysis of optical, near- and mid-IR photometry (ZTF, UKIDSS GPS, NEOWISE) and near-IR spectra (IRTF, Gemini) of the eruptive variable Class I YSO GPSV16. The YSO, associated with the HII region G71.52$-$00.38 ($d=3.61$~kpc), showed two outbursts, one with $ΔK_{\rm s}=2.2$~mag (2005-2012) and a second starting in 2016 with $ΔK_{\rm s}=5.6$~mag and accretion luminosity of $\sim$130 L$_{\odot}$. The outbursts displayed distinct spectroscopic characteristics: the first showed emission lines associated with a hot inner disk surface, whereas the second showed absorption lines arising from the cooler upper layers of a viscously heated disk. These features likely arose due to the different accretion rates reached during each outburst. The second outburst showed a two-stage mid-IR rise, requiring $\approx8.4$ years to reach peak brightness. The mid-IR rise also started 8 years before the onset of the optical outburst. The wavelength-dependent light curve points to an instability that is triggered at larger distances within the accretion disk and propagates inward. Assuming a propagation time of 8 years for the accretion wave, we estimate that the second outburst started at a distance of $r\sim0.4$~AU. These results show how long-term, multi-wavelength photometric monitoring can help identify the disk instabilities that trigger eruptions in YSOs.

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arXiv2025

Refined classification of YSOs and AGB stars by IR magnitudes, colors, and time-domain analysis with machine learning

We introduce a binary classification model, {\it the Double Filter Model}, utilizing various machine learning and deep learning methods to classify Young Stellar Objects (YSOs) and Asymptotic Giant Branch (AGB) stars. Since YSOs and AGB stars share similar infrared (IR) photometric characteristics due to comparable temperatures and the presence of circumstellar dust, distinguishing them is challenging and often leads to misclassification. While machine learning and deep learning techniques have helped reduce YSO-AGB misclassifications, achieving a reliable separation remains challenging. Given that YSOs and AGB stars exhibit distinct light curves resulting from different variability mechanisms, our Double Filter Model leverages light curve data to enhance classification accuracy. This approach uncovered YSOs and AGB stars that were misclassified in IR photometry and was validated against Taurus YSOs and spectroscopically confirmed AGB stars. We applied the model to the {\it Spitzer/IRAC Candidate YSO Catalog for the Inner Galactic Midplane} (SPICY) catalog for catalog refinement and identified potential AGB star contaminants.

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arXiv2025

VVV-WIT-13: an eruptive young star with cool molecular features

Here we investigate an infrared eruptive source, identified from the decade-long VISTA Variables in the Via Lactea survey (VVV). We named this target after a group of variable sources discovered by VVV, as VVV-WIT-13, with WIT standing for "What Is This?", due to its unique photometric variation behaviour and the mysterious origin of the outburst. This target exhibited an outburst with a 5.7 mag amplitude in the Ks-band, remained on its brightness plateau for 3.5 years, and then rapidly faded to its pre-eruptive brightness afterwards. We aim to reveal the variable nature and outburst origin of VVV-WIT-13 by presenting our follow-up photometric and spectroscopic observations along with theoretical models. We gathered photometric time series in both near- and mid-infrared wavelengths. We obtained near-infrared spectra during the outburst and decaying stages on XSHOOTER/VLT and FIRE/Magellan, and then fitted the detected molecular absorption features using models from ExoMol. We applied 2D numerical simulations to re-create the observables of the eruptive phenomenon. We observe deep AlO absorption bands in the infrared spectra of VVV-WIT-13, during the outburst stage, along with other more common absorption bands (e.g. CO). Our best-fit model suggests a 600 K temperature of the AlO absorption band. In the decaying stage, the AlO bands disappeared, whilst broad blue-shifted H2 lines arose, a common indicator of stellar wind and outflow. The observational evidence suggests that the CO and TiO features originate from an outflow or a wind environment. We find that VVV-WIT-13 is an eruptive young star with instability occurring in the accretion disk. One favoured theoretical explanation of this event is a disrupted gas clump at a distance of 3 au from the source. If confirmed, this would be the first such event observed in real time.

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arXiv2025

Submillimeter and Mid-Infrared Variability of Young Stellar Objects in the M17 HII Region

We conducted a comprehensive analysis of young stellar object (YSO) variability at submillimeter and mid-infrared (mid-IR) wavelengths for the M\,17 \ion{H}{2} region, using 3.5 years monitoring data from the JCMT Transient Survey at $450$ and $850\,μ$m and 9 years mid-IR monitoring data from the NEOWISE mission. Our study encompasses observations of 198 and 164 bright submillimeter peaks identified within the deep JCMT coadded maps at 450 and $850\,μ$m, and 66 YSOs seen by NEOWISE W2 that were previously identified in mid-IR observations. We find one robust linear submillimeter variable, an intermediate mass protostar, with a $4\%$ peak flux change in 3.5 years of JCMT monitoring that sets a lower limit of $16\%$ luminosity increase for the source. At mid-IR wavelengths, our analysis reveals secular and stochastic variability in 22 YSOs, with the highest fraction of secular variability occurring at the earliest evolutionary stage. This mid-IR fractional variability as a function of evolutionary stage result is similar to what has previously been found for YSO variability within the Gould Belt and the intermediate-mass star formation region M17\,SWex, though overall less variability is detected in M\,17 in submillimeter and mid-IR. We suspect that this lower detection of YSO variability is due to both the greater distance to M\,17 and the strong feedback from the \ion{H}{2} region. Our findings showcase the utility of multiwavelength observations to better capture the complex variability phenomena inherent to star formation processes and demonstrate the importance of years-long monitoring of a diverse selection of star-forming environments.

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arXiv2025

"Oh FUors where art thou": A search for long-lasting YSO outbursts hiding in infrared surveys

Long-lasting episodes of high accretion can strongly impact stellar and planetary formation. However, the universality of these events during the formation of young stellar objects (YSOs) is still under debate. Accurate statistics of strong outbursts (FUors), are necessary to understand the role of episodic accretion bursts. In this work, we search for a population of FUors that may have gone undetected in the past because they either a) went into outburst before the start of modern monitoring surveys and are now slowly fading back into quiescence or b) are slow-rising outbursts that would not commonly be classified as candidate FUors. We hypothesise that the light curves of these outbursts should be well fitted by linear models with negative (declining) or positive (rising) slopes. The analysis of the infrared light curves and photometry of $\sim$99000 YSO candidates from SPICY yields 717 candidate FUors. Infrared spectroscopy of 20 candidates, from both the literature and obtained by our group, confirms that 18 YSOs are going through long-term outbursts and identifies two evolved sources as contaminants. The number of candidate FUors combined with previously measured values of the frequency of FUor outbursts, yield average outburst decay times that are 2.5 times longer than the rise times. In addition, a population of outbursts with rise timescales between 2000 and 5000 days must exist to obtain our observed number of YSOs with positive slopes. Finally, we estimate a mean burst lifetime of between 45 and 100 years.

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arXiv2025

Sub-Millimeter Variability in the Envelope & Warped Protostellar Disk of the Class 0 Protostar HOPS 358

The JCMT Transient Survey recently discovered that the Class 0 protostar HOPS 358 decreased in 350 GHz continuum brightness by $\sim25$% over the course of four years before brightening again for the next four. The JCMT lightcurve can be fit by a long timescale dip lasting roughly eight years. A shorter timescale periodicity is also apparent with a period of 1.75 years and a small 3% amplitude. NEOWise monitoring reveals that the mid-IR wavelength brightness of HOPS 358 follows a similar long-term pattern in time. Here, we present a study of nine epochs of ALMA observations of HOPS 358 taken over the course of the decline and subsequent rise in brightness seen with the JCMT to test whether the variation seen on $\sim15"$ scales, covering both disk and envelope, is also observed on smaller, $<1"$ scales that primarily probe HOPS 358's protostellar disk. We detect both HOPS 358 and its southern companion, HOPS 358B, in our ALMA observations, and find that at least one of the two is varying. Assuming that HOPS 358 is the variable, the light curve has the same shape as that found by the JCMT. Additionally, our high resolution ALMA imaging of HOPS 358 reveals that the disk is warped, with a $16^{\circ}$ warp at a disk radius of 35 au, about halfway through the extent of the disk. The physical origin of the warp along with how it relates to the variability seen towards HOPS 358, however, remain unclear.

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arXiv2024

On the incidence of episodic accretion in Class I YSOs from VVV

Episodic accretion is one of the competing models to explain the observed luminosity spread in young stellar clusters. These short-lived high accretion events could also have a strong impact on planet formation. Observations of high-amplitude variability in young stellar objects (YSOs) due to large changes in the accretion rate provide direct observational evidence for episodic accretion. However, there are still uncertainties in the frequency of these events and if episodic accretion is universal among YSOs. To determine the frequency of outbursts in Class I YSOs, we built a large and robust sample of objects at this evolutionary stage, and searched for high-amplitude near-infrared ($ΔK_{\rm S}>2$~mag) variability in the VIRAC2 database of the Vista Variables in the Via Lactea (VVV) survey. By complementing with near-IR (2MASS and DENIS) and mid-IR (WISE/Neo-WISE) data, we find that from $\sim$ 7000 Class I YSOs, 97 objects can be classified as eruptive variable YSOs. The duration of the outbursts vary from a few months to longer than 9 years, and cover a similar range of amplitudes. Values of $ΔK_{\rm S}>5$~mag, however, are only observed in outbursts with duration longer than 9 years. When considering different effects of completeness and contamination we estimate that the incidence of episodic accretion in Class I YSOs is between 2\% and 3\%. Finally, we determine a recurrence timescale of long-term outbursts (a.k.a FUors) of $τ=1.75^{+1.12}_{-0.87}$~kyr. The latter value agrees with previous estimates and is in line with the expectations of higher frequency of FUor outbursts during younger stages of evolution.

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arXiv2024

An outburst and FU Ori-type disk of a former low luminosity protostar

Strong accretion outbursts onto protostars are associated with emission dominated by a viscously heated disk, which is characterized by high luminosities. We report the discovery and characterization of a strong mid-IR (3.4, 4.6 $μ$m) outburst in the embedded protostar SSTgbs J21470601+4739394 (hereafter SSTgbsJ214706). SSTgbsJ214706 has steadily brightened in the mid-infrared by $\sim2$ magnitudes over the past decade, as observed by NEOWISE. Follow-up investigations with the Gemini near-IR spectrograph reveal that SSTgbsJ214706 is a binary system with a spatially extended outflow. The outburst is occurring on the more embedded southeast (SE) component, which dominates the mid- and far-infrared emission from the source. The outbursting component exhibits a spectrum consistent with an FU Ori-type outburst, including the presence of enhanced absorption observed in the molecular bands of CO. The luminosity of the SE component is estimated to be $\sim 0.23\,$ L$_\odot$ before the outburst and $\sim 0.95\,$ L$_\odot$ during the outburst, which is 1 to 2 orders of magnitude fainter than bonafide FU Ori outbursts. We interpret this eruption as an FU Ori-type outburst, although the possibility of brightening following an extinction episode cannot be ruled out. We discuss the implications and potential explanations for such a low-luminosity eruption.

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arXiv2023

Mid-Infrared Variability of Young Stellar Objects on Timescales of Days to Years

Variability in the brightness of Young Stellar Objects (YSOs) is a common phenomenon that can be caused by changes in various factors, including accretion, extinction, disk morphology, interactions between the disk and the stellar photosphere, and the rotation of hot or cold magnetic spots on the stellar photosphere. Analyzing the variability on different timescales gives insight into the mechanisms driving the brightness changes in YSOs. We investigate the variability of YSOs on both long and short timescales using two mid-infrared datasets: the NEOWISE 7.5-year W2 (4.6$μ$m) data and the YSOVAR 40-day Spitzer/IRAC2 (4.5$μ$m) data, respectively. We classify the variability types in each timescale following Park et al (2021). We find a higher detection rate of variable sources in the short-term (77.6%) compared to the long-term (43.0%) due to the higher sensitivity of the Spitzer observations. In addition, the higher cadence of the YSOVAR data results in the weeks-long short-term variability being mostly secular, while the years-long long-term variability explored with the coarsely sampled NEOWISE data is mostly stochastic. By cross-matching the two catalogs, we statistically analyze the variability types exhibited by YSOs across both timescales. The long-term variability amplitude is mostly three times (up to ten times) greater than the short-term variability. Furthermore, we evaluate variability on very short (1-2 days) timescales and recover a trend of the increasing amplitude of variability as the timescales increase. By comprehensively analyzing the variability of YSOs over various timescales, we contribute to a deeper understanding of the underlying mechanisms driving their variability.

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arXiv2023

The CO outflow components ejected by a recent accretion event in B335

Protostellar outflows often present a knotty appearance, providing evidence of sporadic accretion in stellar mass growth. To understand the direct relation between mass accretion and ejection, we analyze the contemporaneous accretion activity and associated ejection components in B335. B335 has brightened in the mid-IR by 2.5 mag since 2010, indicating increased luminosity, presumably due to increased mass accretion rate onto the protostar. ALMA observations of 12CO emission in the outflow reveal high-velocity emission, estimated to have been ejected 4.6 - 2 years before the ALMA observation and consistent with the jump in mid-IR brightness. The consistency in timing suggests that the detected high-velocity ejection components are directly linked to the most recent accretion activity. We calculated the kinetic energy, momentum, and force for the ejection component associated with the most recent accretion activity and found that at least, about 1.0% of accreted mass has been ejected. More accurate information on the jet inclination and the temperature of the ejected gas components will better constrain the ejected mass induced by the recently enhanced accretion event.

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arXiv2023

Photometric and Spectroscopic monitoring of YSOs in nearby star forming regions. I. Eruptive YSOs

Mid-infrared (mid-IR) variability in young stellar objects (YSOs) is driven by several physical mechanisms, which produce a variety of amplitudes and light curve shapes. One of these mechanisms, variable disk accretion is predicted by models of episodic accretion to drive secular variability, including in the mid-IR. Because the largest accretion bursts are rare, adding new objects to the YSO eruptive variable class aids our understanding of the episodic accretion phenomenon and its possible impact on stellar and planetary formation. A previous analysis of 6.5 yr of NeoWISE light curves (3-5 $μ$m) of ~7000 nearby YSOs found an increase in the fraction of variability and variability amplitude for objects at younger stages of evolution. To help interpret these light curves, we have obtained low- and high-resolution near-IR spectra of 78 objects from this sample of YSOs. In this work, we present the analysis of nine nearby YSOs (d$<$1 kpc) that show the characteristics of known classes of eruptive variable YSOs. We find one FUor-like source, one EX Lupi-type object, and six YSOs with mixed characteristics, or V1647 Ori-like objects. The varied characteristics observed in our sample are consistent with recent discoveries of eruptive YSOs. We discuss how a wide range in YSO outburst parameters (central mass, maximum accretion rate during outburst, evolutionary stage and/or instability leading to the outburst) may play a significant role in the observed spectro-photometric properties of YSO outbursts.

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arXiv2022

Dissecting the different components of the modest accretion bursts of the very young protostar HOPS 373

Observed changes in protostellar brightness can be complicated to interpret. In our JCMT~Transient monitoring survey, we discovered that a young binary protostar, HOPS 373, is undergoing a modest $30\%$ brightness increase at 850 $μ$m, caused by a factor of 1.8$-$3.3 enhancement in the accretion rate. The initial burst occurred over a few months, with a sharp rise and then shallower decay. A second rise occurred soon after the decay, and the source is still bright one year later. The mid-IR emission, the small-scale CO outflow mapped with ALMA, and the location of variable maser emission indicate that the variability is associated with the SW component. The near-infrared and NEOWISE $W1$ and $W2$ emission is located along the blueshifted CO outflow, spatially offset by $\sim3$ to $4^{\prime\prime}$ from the SW component. The $K$-band emission imaged by UKIRT shows a compact H$_2$ emission source at the edge of the outflow, with a tail tracing the outflow back to the source. The $W1$ emission, likely dominated by scattered light, brightens by 0.7 mag, consistent with expectations based on the sub-mm lightcurve. The signal of continuum variability in $K$-band and $W2$ is masked by stable H$_2$ emission, as seen in our Gemini/GNIRS spectrum, and perhaps by CO emission. These differences in emission sources complicate infrared searches for variability of the youngest protostars.

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arXiv2021

Quantifying Variability of YSOs in the Mid-IR Over Six Years with NEOWISE

Variability in young stellar objects (YSOs) can be caused by various time-dependent phenomena associated with star formation, including accretion rates, geometric changes in the circumstellar disks, stochastic hydromagnetic interactions between stellar surfaces and inner disk edges, reconnections within the stellar magnetosphere, and hot/cold spots on stellar surfaces. We uncover and characterize $\sim$1700 variables from a sample of $\sim$5400 YSOs in nearby low-mass star-forming regions using mid-IR light curves obtained from the 6.5-years NEOWISE All Sky Survey. The mid-IR variability traces a wide range of dynamical, physical, and geometrical phenomenon. We classify six types of YSO mid-IR variability based on their light curves: secular variability ($Linear, Curved, Periodic$) and stochastic variability ($Burst, Drop, Irregular$). YSOs in earlier evolutionary stages have higher fractions of variables and higher amplitudes for the variability, with the recurrence timescale of FUor-type outbursts (defined here as $Δ$W1 or $Δ$W2 $>1$ mag followed by inspection of candidates) of $\sim$1000 years in the early embedded protostellar phase. Known eruptive young stars and subluminous objects show fractions of variables similar to the fraction ($\sim55\%$) found in typical protostars, suggesting that these two distinct types are not distinct in variability over the 6.5-year timescale. Along with brightness variability, we also find a diverse range of secular color variations, which can be attributed to a competitive interplay between the variable accretion luminosity of the central source and the variable extinction by material associated with the accretion process.

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arXiv2021

AGB interlopers in YSO catalogues hunted out by NEOWISE

AGBs and YSOs often share the same domains in IR color-magnitude or color-color diagrams leading to potential mis-classification. We extracted a list of AGB interlopers from the published YSO catalogues using the periodogram analysis on NEOWISE time series data. YSO IR variability is typically stochastic and linked to episodic mass accretion. Furthermore, most variable YSOs are at an early evolutionary stage, with significant surrounding envelope and/or disk material. In contrast, AGBs are often identified by a well defined sinusoidal variability with periods of a few hundreds days. From our periodogram analysis of all known low mass YSOs in the Gould Belt, we find 85 AGB candidates, out of which 62 were previously classified as late-stage Class III YSOs. Most of these new AGB candidates have similar IR colors to O-rich AGBs. We observed 73 of these AGB candidates in the H2O, CH3OH and SiO maser lines to further reveal their nature. The SiO maser emission was detected in 10 sources, confirming them as AGBs since low mass YSOs, especially Class III YSOs, do not show such maser emission. The H2O and CH3OH maser lines were detected in none of our targets.

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arXiv2020

Young Faithful: The Eruptions of EC 53 as It Cycles through Filling and Draining the Inner Disk

While young stellar objects sometimes undergo bursts of accretion, these bursts usually occur sporadically, making them challenging to study observationally and to explain theoretically. We build a schematic description of cyclical bursts of the young stellar object EC 53 using near-IR and sub-mm monitoring obtained over six cycles, each lasting $\approx530$ days. EC 53 brightens over $0.12$ yr by $0.3$ mag at 850 $μ$m, $2$ mag at 3.35 $μ$m, and $1.5$ mag at near-IR wavelengths, to a maximum luminosity consistent with an accretion rate of $\sim8\times10^{-6}$ M$_\odot$ yr$^{-1}$. The emission then decays with an e-folding timescale of $\approx0.74$ yr until the accretion rate is $\sim1\times10^{-6}$ M$_\odot$ yr$^{-1}$. The next eruption then occurs, likely triggered by the buildup of $\sim5\times10^{-6}$ M$_\odot$ of mass in the inner disk, enough that it becomes unstable and drains onto the star. Just before outburst, when the disk is almost replenished, the near-IR colors become redder, indicating an increase in the geometrical height of the disk by this mass buildup. The reddening disappears soon after the initial burst, as much of the mass is drained from the disk. We quantify physical parameters related to the accretion process in EC 53 by assuming an $α$-disk formulation, constrained by the observed disk properties and accretion rate. While we can only speculate about the possible trigger for these faithful eruptions, we hope that our quantified schematic will motivate theorists to test the hypothesized mechanisms that could cause the cyclical buildup and draining of mass in the inner disk.

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arXiv2020

The Relationship between Mid-Infrared and Sub-Millimetre Variability of Deeply Embedded Protostars

We study the relationship between the mid-infrared and sub-mm variability of deeply embedded protostars using the multi-epoch data from the Wide Infrared Survey Explorer ($WISE$/NEOWISE) and the ongoing James Clerk Maxwell Telescope (JCMT) transient survey. Our search for signs of stochastic (random) and/or secular (roughly monotonic in time) variability in a sample of 59 young stellar objects (YSOs) revealed that 35 are variable in at least one of the two surveys. This variability is dominated by secular changes. Of those objects with secular variability, 14 objects ($22\%$ of the sample) show correlated secular variability over mid-IR and sub-mm wavelengths. Variable accretion is the likely mechanism responsible for this type of variability. Fluxes of YSOs that vary in both wavelengths follow a relation of $\log_{10} F_{4.6}(t)=η\log_{10} F_{850}(t)$ between the mid-IR and sub-mm, with $η=5.53\pm0.29$. This relationship arises from the fact that sub-mm fluxes respond to the dust temperature in the larger envelope whereas the mid-IR emissivity is more directly proportional to the accretion luminosity. The exact scaling relation, however, depends on the structure of the envelope, the importance of viscous heating in the disc, and dust opacity laws.

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arXiv2018

Gaia 17bpi: An FU Ori Type Outburst

We report on the source Gaia 17bpi and identify it as a new, ongoing FU Ori type outburst, associated with a young stellar object. The optical lightcurve from Gaia exhibited a 3.5 mag rise with the source appearing to plateau in mid/late 2018. Mid-infrared observations from NEOWISE also show a $>$3 mag rise that occurred in two stages, with the second one coincident with the optical brightening, and the first one preceding the optical brightening by $\sim$1.5 years. We model the outburst as having started between October and December of 2014. This wavelength-dependent aspect of young star accretion-driven outbursts has never been documented before. Both the mid-infrared and the optical colors of the object become bluer as the outburst proceeds. Optical spectroscopic characteristics in the outburst phase include: a GK-type absorption spectrum, strong wind/outflow in e.g. Mgb, NaD, H$α$, KI, OI, and CaII profiles, and detection of LiI 6707 Å. The infrared spectrum in the outburst phase is similar to that of an M-type spectrum, notably exhibiting prominent $H_2O$ and $^{12}$CO (2-0) bandhead absorption in the K-band, and likely HeI wind in the Y-band. The new FU Ori source Gaia 17bpi is associated with a little-studied dark cloud in the galactic plane, located at a distance of 1.27 kpc.

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