arXiv subjects

Fernando Cruz-Sáenz de Miera

Publications and source records attributed to Fernando Cruz-Sáenz de Miera.

At least 19 recordsLinked to original sources

arXiv2026

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) VI. Discovery of a class I methanol maser transition and its association with acetaldehyde

CH3OH masers that are collisionally pumped, referred to as `class I', commonly trace shock interfaces in star-forming regions, but their incidence in low-mass protostars remains poorly quantified. We use data from the COMPASS ALMA Large Program to establish the occurrence, spatial origin, and excitation of a newly detected class I CH3OH maser at 302.9 GHz towards low-mass protostars and to test whether its pumping environments exhibit signatures of shock-driven complex chemistry. COMPASS provides unbiased line surveys of 11 sources between 279.0 and 311.7 GHz at typical angular resolutions of 0.3"-0.5". Rotation diagram analysis of departures from LTE in the 302.9 GHz CH3OH excitation robustly reveals masing in seven of 11 sources, with peak brightness temperatures from a few to ~10^3 K. The brightest detection is towards HOPS 108 and is likely associated with the powerful outflow from the nearby intermediate-mass protostar HOPS 370. Excluding this case, the maser is detected in six of ten low-mass protostars (60%). All six are Class 0 sources interacting with dense ambient material, whereas the non-detections comprise three Class I sources and one isolated Class 0 core, indicating a preference for early evolutionary stages and gas-rich environments for outflow-ambient medium interactions. The maser emission is spatially coincident with thermal CH3OH along outflow cavity walls and bow shocks, but is more compact and knot-like. Among the surveyed COMs, only CH3CHO closely traces the shocked morphology of the 302.9 GHz maser, and only around HOPS 108. These results show that class I CH3OH masers in low-mass protostellar systems are more prevalent than previously recognised and preferentially occur in younger, more embedded sources. More sensitive CH3CHO observations are needed to test whether a similar relationship with shock-driven chemistry also applies in the low-mass regime.

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arXiv2026

Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) II. Approach to data reduction and products for line-rich broadband (sub)millimeter spectra

Studying the chemical composition of the warm gas surrounding embedded solar-type protostars is one of the areas for which the Atacama Large Millimeter/submillimeter Array (ALMA) is particularly well suited. Recently, the ALMA Large Program ``Complex Organic Molecules in Protostars with ALMA Spectral Surveys'' (COMPASS) carried out an observing campaign of a sample of 11 protostellar regions to investigate the chemical impact of their environments and evolutionary stages. The aim of this paper is to provide the observational and procedural information necessary for the community to understand the analysis presented in forthcoming scientific papers by the COMPASS collaboration, and to enable archival research using the data products provided by our team and the ALMA Science Archive. This paper describes the technical setup of the observations, and it outlines the data-processing pipeline and primary data products from this initiative. The Common Astronomy Software Applications (CASA) was used for initial calibration following the standard ALMA Pipeline, and then IMAGER was used for self-calibration and imaging. We describe post-processing done with Python to achieve favorable continuum subtraction, correct for the primary beam response, and extract spectra. We discuss our strategy for mitigating data challenges, including those related to data volume and continuum subtraction for spectral line analysis. The incorporation of IMAGER in our workflow was advantageous in terms of the computing efficiency which allowed us to benchmark several imaging parameters and techniques; we also demonstrate that the imaging outcomes using IMAGER or CASA are scientifically comparable. Numerous data products are generated for the program, including image cubes for the 36 spectral windows targeting each source, extracted spectra, and continuum images.

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arXiv2026

Gaia21bja: pre-main sequence star with quasi-periodic bursts

Gaia21bja is a Gaia alerted young stellar object (YSO) that exhibits at least seven quasi-peridoic brightenings over a 20 year-long light curve with durations of 1.5-2 years and amplitudes up to $\sim$1.7 mag in the Gaia $G$-band. We analyze its optical and near-infrared photometry and spectra taken using the IRTF and VLT in its faint and bright states in order to characterize its physical properties. A Lomb-Scargle periodogram analysis results in a most significant period of $916\pm77$ days. We derived the stellar parameters as $R_\star= 0.78 \pm 0.04~R_\odot$, $L_\star=(4.5\pm0.3) \times 10^{-2}~L_\odot$, and $M_\star= 0.16 \pm 0.03~M_\odot$. The spectra taken during the burst are dominated by emission lines and are similar to those of EX Lupi-type eruptive young stars (EXors). We found that the accretion luminosity and mass accretion rate increased by a factor of $5.5-6$ during the burst. Based on this, and the quasi-periodic bursts, we suggest that Gaia21bja is an eruptive YSO, and is most consistent with the `Periodic' category of the Outbursting YSOs Catalogue.

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arXiv2026

Gaia20dsk: A new MNor discovered by the GLORIOUS collaboration

Context. Among known young stellar objects (YSOs), those exhibiting the most dramatic increases in brightness due to sudden increase in mass accretion rate are eruptive young stars. Gaia20dsk is one of the Gaia-alerted young star candidates that has displayed a double, nonperiodic brightening resembling that of other young eruptive stars. Aims. The goal of this work is to determine the physical and accretion properties of Gaia20dsk to confirm its classification as an eruptive young star. Methods. We combined publicly available optical and near-infrared (NIR) photometry with our X-shooter optical/NIR spectrum. In our analysis, we examined the optical and IR light curves from the bursts, reviewing the color-magnitude diagrams across different bands, reporting the detection of emission lines, and providing estimates of the star's accretion rates during the burst. Results. The optical light curve shows two major and one brief brightening events with a maximum amplitude of ~1.8 mag in the last five years. A classification based on spectral index indicates that Gaia20dsk is a flat-spectrum star. The X-shooter spectrum exhibit emission lines characteristic of accreting low-to-intermediate-mass young stars, displaying features typical of MNor-type objects. The mass accretion rate is between (0.5-1.8)*10^{-6} M_sun/yr. Conclusions. Gaia20dsk is an eruptive YSO that exhibits photometric features similar to those of MNors, including its characteristic brightening amplitude and burst duration, along with similar spectroscopic features and accretion rates.

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arXiv2025

The evolution of complex organic molecules during star formation

Complex organic molecules (COMs) are thought to be the precursors of pre-biotic molecules and are observed in many protostellar sources. For this paper we studied the formation of COMs during star formation and their evolution in the midplane of the circumstellar disk up to the end of the Class I stage. We used the Analytical Protostellar Environment (APE) code to perform analytical simulations of star formation and the Nautilus code to model the chemical evolution. Most COMs mainly form during the collapse or in the disk, except the lightest (CH3CCH, C3H6, CH3OH, CH3CHO, CH3OCH3, C2H5OH, CH3CN, CH3NC, C2H3CN, and CH3SH), which are significantly inherited by the disk from the prestellar phase. Over the first 150 kyr of the disk, the abundances of several COMs in the midplane vary negligibly (e.g., CH3CCH, CH3OH, and CH3CN), while others experience a variation of one order of magnitude (e.g., C2H3CHO HOCH2CHO, and CH3COCH2OH). Changing physical conditions also have an impact on the abundance profiles of COMs in the disk, and their inheritance. For example, increasing the temperature of the molecular cloud from 10 K to 15 K significantly promotes the formation of COMs in the prestellar phase, notably c-C2H4O and N-bearing species. Conversely, increasing the cloud mass from 2 Msol to 5 Msol only has a minor effect on the disk abundances in the early stages.

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arXiv2025

APE: An analytical protostellar environment to provide physical conditions to chemical models and synthetic observations

Chemical modeling and synthetic observations are powerful methods to interpret observations, both requiring a knowledge of the physical conditions. In this paper, we present the Analytical Protostellar Environment (APE) code, which aims at making chemical simulations and synthetic observations accessible. APE contains a physical model of protostellar evolution (including the central object, the envelope, the protoplanetary disk and the outflow) as well as interfaces to publicly available codes to perform chemical simulations, radiative transfer calculations, and synthetic interferometry imaging. APE produces density and temperature maps of protostellar systems. The code can also follow individual particles throughout their journey in a collapsing core. APE includes a treatment of the dust grain size-distribution to compute opacities self-consistently for subsequent radiative transfer. We show an example of application of APE by computing chemical abundance maps of CO, CN, CS, H2CO, and CH3OH in a Class I protostellar system. We also performed synthetic ALMA observations of their molecular emission assuming an edge-on source inclination. The moment 0 maps of CO, CS, and H2CO display an X-shaped emission similar to what is observed toward the Class I source IRAS 04302+2247.

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arXiv2025

The 2023 outburst of the Gaia alerted EXor Gaia23bab

Episodic accretion is a fundamental process in the build-up of the stellar mass. EX Lupi-type eruptive young stars (EXors) represent one of the main types of episodic accretion. We study the recently discovered EXor Gaia23bab during its 2023 outburst. We obtained optical and near-infrared photometry and spectroscopy to probe the variation of the physical properties of Gaia23bab during its recent outburst. We also collected archival photometry to study a previous outburst of the star. We used several accretion tracers, including the Ca II triplet, He I, and various hydrogen lines from the Paschen and Brackett series, to measure the accretion rate during the outburst. The accretion rate is consistent with $\sim 2.0 \times 10^{-7} M_\odot$ $\rm{yr}^{-1}$. Comparing the line fluxes of the hydrogen Brackett series to predictions of Case B theory suggests excitation temperatures of 5000 - 10000 K and electron densities of $10^9$-$10^{10}$ cm$^{-3}$. Comparison to the predictions of a model for T Tauri stars revealed that the fluxes of the Balmer series are consistent with temperatures of 5000 - 12500 K and a hydrogen density of $10^8$ cm$^{-3}$, while the fluxes of the Paschen series are consistent with temperatures in the range between 10000 and 12500 K and a hydrogen density of $10^{11}$ cm$^{-3}$. The derived temperatures and densities confirm that Gaia23bab is a prototypical EXor, not only due to its accretion rate, but also based on the best fit temperatures and densities revealed by the detected hydrogen lines.

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arXiv2025

A Multi-Wavelength Study of the Dynamic Environment surrounding the FUor V960 Mon

The evolution of young stars and planet-forming environments is intrinsically linked to their nascent surroundings. This is particularly evident for FU Orionis (FUor) objects$-$a class of young protostars known for dramatic outbursts resulting in significant increases in brightness. We present a case study of V960 Mon, an FUor that has recently been found to show signs of a fragmenting spiral arm, potentially connected to planet formation. Our study explores the large-scale environment ($10^3-10^4$ au) and incorporates ALMA band 3, band 4 and band 6 continuum data, molecular emissions from $^{12}$CO, $^{13}$CO, C$^{18}$O, SiO, DCO$^+$, N$_2$D$^+$ and DCN, alongside optical and near-infrared observations from VLT/MUSE and VLT/SPHERE. We map a region of 20" across where we find tantalizing emissions that provide a unique view of a young group of protostars, including the discovery of a class-0 protostar to the east of the FUor. The $^{12}$CO and SiO tracers suggest that this object is at the base of an outflow, potentially impacting the surrounding medium. The MUSE and SPHERE observations indicate the presence of an elongated feature towards a prominent source to the southeast that may represent interaction between V960 Mon and its surrounding. Moreover, the C$^{18}$O emission overlaps with the clumps of the detected fragmenting spiral arm. These findings provide the strongest evidence to date for a connection between infalling material, fragmentation, and the intensity outburst of a protostar. Our case study highlights the complex interactions between young stars and their surroundings that drive the evolution of the planet forming environment.

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arXiv2025

The hot corino-like chemistry of four FUor-like protostars

Context: Compared to Class 0 protostars, the higher densities and lower temperatures of the disk midplanes of Class I young stellar objects (YSOs) limit the detectability of complex organic molecules (COMs). The elevated luminosities of eruptive YSOs increase disk temperatures sublimating frozen molecules and easing their detection. Aims: Our aim is to investigate the chemical composition of four FUor-like Class I YSOs: L1551 IRS 5, Haro 5a IRS, V346 Nor, and OO Ser, and to compare their abundances of COMs with other YSOs in the literature. Methods: We search for COMs line emission in ALMA Band 6 observations. We use the CASSIS software to determine their column densities (N) and excitation temperatures (T_ex) assuming local thermodynamical equilibrium. Results: We detect 249 transitions from 12 COMs. In L1551 IRS 5 we identified CH3OH, 13CH3OH, CH318OH, CH2DOH, CH3CHO, CH3OCH3, CH3OCHO, CH3COCH3, C2H5OH, C2H5CN, 13CH3CN, and CH3C15)N. Haro 5a IRS and OO Ser have emission from CH3OH, CH3CHO, CH3OCH3, and CH3OCHO. CH3COCH3 is also detected in OO Ser. In V346 Nor we found CH3OH, CH2DOH, CH3CHO, CH3OCH3, CH3OCHO, and C2H5CN. The emission of COMs is compact in all targets. The analysis indicates their temperatures are above 100K. The abundance ratios of COMs derived for these eruptive YSOs, as well as for other protostars in the literature, span several orders of magnitude without any clear differentiation between the eruptive and quiescent YSOs. The column density of the main isotopologue of CH3OH should not be used as a reference, as most of the lines are optically thick. Conclusions: The hot and compact emission of COMs indicates that the four FUor-like targets are hot corino-like. Spectral studies of such objects can be useful to investigate the complex organic chemistry at later evolutionary stages than the usual Class 0 stage.

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arXiv2025

Evidence for an accretion bridge in the DX Cha circumbinary system from VLTI/MATISSE observations

DX Cha (HD 104237) is a spectroscopic binary consisting of a Herbig A7.5Ve-A8Ve primary star and a K3-type companion. Here we report on new $3.55$ micrometer interferometric observations of this source with the Multi Aperture Mid-Infrared Spectroscopic Experiment (MATISSE) at the Very Large Telescope Interferometer (VLTI). To model the four MATISSE observations obtained between 2020 and 2023, we constructed a time-dependent interferometric model of the system, using the oimodeler software. The model consists of an asymmetric ring and two point sources on a Keplerian orbit. Our best-fit model consists of a circumbinary ring with a diameter of $0.86$ au ($8.1$ mas), featuring a strong azimuthal asymmetry. We found that the position angle of the asymmetry changes tens of degrees between the MATISSE epochs. The ring is relatively narrow, with a full width at half maximum (FWHM) of $\sim$$0.13$ au ($1.23$ mas). The presence of circumstellar dust emission so close to the binary is unexpected, as previous hydrodynamic simulations predicted an inner disk cavity with a diameter of $\sim$$4$ au ($\sim$$37.5$ mas). Thus, we argue that the narrow envelope of material we detected is probably not a gravitationally stable circumbinary ring, but may be part of tidal accretion streamers channeling material from the inner edge of the disk toward the stars.

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arXiv2023

A high HDO/H$_{2}$O ratio in the Class I protostar L1551 IRS5

Water is a very abundant molecule in star-forming regions. Its deuterium fractionation is an important tool for understanding its formation and evolution during the star and planet formation processes. While the HDO/H$_2$O ratio has been determined toward several Class 0 protostars and comets, the number of studies toward Class I protostars is limited. We aim to study the water deuteration toward the Class I binary protostar L1551 IRS5 and to investigate the effect of evolutionary stage and environment on variations in the water D/H ratio. Observations were made using the NOEMA interferometer. The HDO 3$_{1,2}$-2$_{2,1}$ transition at 225.9 GHz and the H$_2^{18}$O 3$_{1,3}$-2$_{2,0}$ transition at 203.4 GHz were covered with a spatial resolution of 0.5'' $\times$ 0.8'', while the HDO 4$_{2,2}$-4$_{2,3}$ transition at 143.7 GHz was observed with a resolution of 2.0'' $\times$ 2.5''. We used both LTE and non-LTE models. The three transitions are detected. The line profiles display two peaks, one at $\sim$6 km s$^{-1}$ and one at $\sim$9 km s$^{-1}$. We derive an HDO/H$_2$O ratio of (2.1 $\pm$ 0.8) $\times$ 10$^{-3}$ for the redshifted component and a lower limit of $>$ 0.3 $\times$ 10$^{-3}$ for the blueshifted component due to the blending with the redshifted CH$_3$OCH$_3$ emission. The HDO/H$_2$O in L1551 IRS5 is similar to the ratios in isolated Class 0 sources and to the Class I V883 Ori, while it is significantly higher than in the clustered Class 0 sources and the comets. This suggests that the chemistry of protostars in low source densities clouds share more similarities with the isolated sources than the protostars of very dense clusters. If Class 0 protostars with few sources around and isolated Class 0 objects are comparable in the HDO/H$_2$O ratio, it would mean that there is little water reprocessing from the Class 0 to Class I protostellar stage.

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arXiv2023

Gaia21bty: An EXor lightcurve exhibiting an FUor spectrum

Gaia21bty, a pre-main sequence star that previously had shown aperiodic dips in its light curve, underwent a considerable $ΔG\approx2.9$ mag brightening that occurred over a few months between 2020 October - 2021 February. The Gaia lightcurve shows that the star remained near maximum brightness for about $4-6$ months, and then started slowly fading over the next 2 years, with at least three superimposed $\sim$1 mag sudden rebrightening events. Whereas the amplitude and duration of the maximum is typical for EXors, optical and near-infrared spectra obtained at the maximum are dominated by features which are typical for FUors. Modelling of the accretion disc at the maximum indicates that the disc bolometric luminosity is 43 L$_{\odot}$ and the mass accretion rate is $2.5\times10^{-5}$ M$_{\odot}$ yr$^{-1}$, which are typical values for FUors even considering the large uncertainty in the distance ($1.7_{-0.4}^{+0.8}$ kpc). Further monitoring is necessary to understand the cause of the quick brightness decline, the rebrightening, and the other post-outburst light changes, as our multi-colour photometric data suggest that they could be caused by a long and discontinuous obscuration event. We speculate that the outburst might have induced large-scale inhomogeneous dust condensations in the line of sight leading to such phenomena, whilst the FUor outburst continues behind the opaque screen.

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arXiv2023

The Gaia alerted fading of the FUor-type star Gaia21elv

FU Orionis objects (FUors) are eruptive young stars, which exhibit outbursts that last from decades to a century. Due to the duration of their outbursts, and to the fact that only about two dozens of such sources are known, information on the end of their outbursts is limited. Here we analyse follow-up photometry and spectroscopy of Gaia21elv, a young stellar object, which had a several decades long outburst. It was reported as a Gaia science alert due to its recent fading by more than a magnitude. To study the fading of the source and look for signatures characteristic of FUors, we have obtained follow-up near infrared (NIR) spectra using Gemini South/IGRINS, and both optical and NIR spectra using VLT/X-SHOOTER. The spectra at both epochs show typical FUor signatures, such as a triangular shaped $H$-band continuum, absorption-line dominated spectrum, and P Cygni profiles. In addition to the typical FUor signatures, [OI], [FeII], and [SII] were detected, suggesting the presence of a jet or disk wind. Fitting the spectral energy distributions with an accretion disc model suggests a decrease of the accretion rate between the brightest and faintest states. The rapid fading of the source in 2021 was most likely dominated by an increase of circumstellar extinction. The spectroscopy presented here confirms that Gaia21elv is a classical FUor, the third such object discovered among the Gaia science alerts.

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arXiv2023

The clumpy structure of $ε$ Eridani's debris disc revisited by ALMA

$ε$ Eridani is the closest star to our Sun known to host a debris disc. Prior observations in the (sub-)millimetre regime have potentially detected clumpy structure in the disc and attributed this to interactions with an (as yet) undetected planet. However, the prior observations were unable to distinguish between structure in the disc and background confusion. Here we present the first ALMA image of the entire disc, which has a resolution of 1.6"$\times$1.2". We clearly detect the star, the main belt and two point sources. The resolution and sensitivity of this data allow us to clearly distinguish background galaxies (that show up as point sources) from the disc emission. We show that the two point sources are consistent with background galaxies. After taking account of these, we find that resolved residuals are still present in the main belt, including two clumps with a $>3σ$ significance -- one to the east of the star and the other to the northwest. We perform $n$-body simulations to demonstrate that a migrating planet can form structures similar to those observed by trapping planetesimals in resonances. We find that the observed features can be reproduced by a migrating planet trapping planetesimals in the 2:1 mean motion resonance and the symmetry of the most prominent clumps means that the planet should have a position angle of either ${\sim10^\circ}$ or ${\sim190^\circ}$. Observations over multiple epochs are necessary to test whether the observed features rotate around the star.

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arXiv2023

JWST/MIRI Spectroscopy of the Disk of the Young Eruptive Star EX Lup in Quiescence

EX Lup is a low-mass pre-main sequence star that occasionally shows accretion-related outbursts. Here, we present JWST/MIRI medium resolution spectroscopy obtained for EX Lup fourteen years after its powerful outburst. EX Lup is now in quiescence and displays a Class II spectrum. We detect a forest of emission lines from molecules previously identified in infrared spectra of classical T Tauri disks: H2O, OH, H2, HCN, C2H2, and CO2. The detection of organic molecules demonstrates that they are back after disappearing during the large outburst. Spectral lines from water and OH are for the first time de-blended and will provide a much improved characterization of their distribution and density in the inner disk. The spectrum also shows broad emission bands from warm, sub-micron size amorphous silicate grains at 10 and 18 um. During the outburst, in 2008, crystalline forsterite grains were annealed in the inner disk within 1 au, but their spectral signatures in the 10 um silicate band later disappeared. With JWST we re-discovered these crystals via their 19.0, 20.0, and 23.5 um emission, whose strength implies that the particles are at ~3 au from the star. This suggests that crystalline grains formed in 2008 were transported outwards and now approach the water snowline, where they may be incorporated into planetesimals. Containing several key tracers of planetesimal and planet formation, EX Lup is an ideal laboratory to study the effects of variable luminosity on the planet-forming material and may provide explanation for the observed high crystalline fraction in solar system comets.

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arXiv2023

An APEX study of molecular outflows in FUor-type stars

FU Orionis-type objects (FUors) are low-mass pre-main-sequence objects which go through a short-lived phase (~100 years) of increased mass accretion rate (from 10^-8 to 10^-4 M_sun yr^-1). These eruptive young stars are in the early stages of stellar evolution and, thus, still deeply embedded in a massive envelope that feeds material to the circumstellar disk that is then accreted onto the star. Some FUors drive molecular outflows, i.e. low-velocity wide-angle magneto-hydrodynamical winds, that inject energy and momentum back to the surrounding envelopes, and help clear the material surrounding the young star. Here we present a 12CO (3--2), 13CO (3--2) and 12CO (4--3) survey of 20 FUor-type eruptive young stars observed with APEX. We use our 13CO (3--2) observations to measure the masses of the envelopes surrounding each FUor and find an agreement with the FUor evolutionary trend found from the 10um silicate feature. We find outflows in 11 FUors, calculate their masses and other kinematic properties, and compare these with those of outflows found around quiescent young stellar objects gathered from the literature. This comparison indicates that outflows in FUors are more massive than outflows in quiescent sources, and that FUor outflows have a higher ratio outflow mass with respect to the envelope than the quiescent sample, indicating that the eruptive young stars have lower star-forming efficiencies. Finally, we found that the outflow forces in FUors are similar to those of quiescent young stellar objects, indicating that their accretion histories are similar or that the FUor outflows have lower velocities.

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arXiv2022

Photometric and spectroscopic study of the EXor-like eruptive young star Gaia19fct

Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multi-filter optical and near-infrared photometry, as well as near-infrared spectroscopy, to understand the physical properties of Gaia19fct and investigate whether it fits into the historically defined two classes. We present the analyses of light curves, color variations, spectral lines, and CO modeling. The light curves show at least five brightening events since 2015, and the multi-filter color evolutions are mostly gray. The gray evolution indicates that bursts are triggered by mechanisms other than extinction. Our near-infrared spectra exhibit both absorption and emission lines and show time-variability throughout our observations. We found lower rotational velocity and lower temperature from the near-infrared atomic absorption lines than from the optical lines, suggesting that Gaia19fct has a Keplerian rotating disk. The CO overtone features show a superposition of absorption and emission components, which is unlike other young stellar objects. We modeled the CO lines, and the result suggests that the emission and absorption components are formed in different regions. We found that although Gaia19fct exhibits characteristics of both types of eruptive young stars, FU Orionis-type objects (FUors) and EX Lupi-type objects (EXors), it shows more similarity with EXors in general.

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arXiv2022

Photometric and spectroscopic study of the burst-like brightening of two Gaia-alerted young stellar objects

Young stars show variability on different time-scales from hours to decades, with a range of amplitudes. We studied two young stars, which triggered the Gaia Science Alerts system due to brightenings on a time-scale of a year. Gaia20bwa brightened by about half a magnitude, whereas Gaia20fgx brightened by about two and half magnitudes. We analyzed the Gaia light curves, additional photometry, and spectra taken with the Telescopio Nazionale Galileo and the Gran Telescopio Canarias. Several emission lines were detected toward Gaia20bwa, including hydrogen lines from H$α$ to H$δ$, Pa$β$, Br$γ$, and lines of Ca II, O I, and Na I. The H$α$ and Br$γ$ lines were detected toward Gaia20fgx in emission in its bright state, with additional CO lines in absorption, and the Pa$β$ line with an inverse P Cygni profile during its fading. Based on the Br$γ$ lines the accretion rate was $(2.4-3.1)\times10^{-8}$ $M_\odot$ yr$^{-1}$ for Gaia20bwa and $(4.5-6.6)\times10^{-8}$ $M_\odot$ yr$^{-1}$ for Gaia20fgx during their bright state. The accretion rate of Gaia20fgx dropped by almost a factor of 10 on a time-scale of half a year. The accretion parameters of both stars were found to be similar to those of classical T Tauri stars, lower than those of young eruptive stars. However, the amplitude and time-scale of these brightenings place these stars to a region of the parameter space, which is rarely populated by young stars. This suggests a new class of young stars, which produce outbursts on a time-scale similar to young eruptive stars, but with smaller amplitudes.

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