19 research outputs found
A high HDO/HO 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/HO
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 3-2 transition at 225.9 GHz and the HO
3-2 transition at 203.4 GHz were covered with a spatial
resolution of 0.5'' 0.8'', while the HDO 4-4
transition at 143.7 GHz was observed with a resolution of 2.0'' 2.5''.
We used both LTE and non-LTE models. The three transitions are detected. The
line profiles display two peaks, one at 6 km s and one at 9
km s. We derive an HDO/HO ratio of (2.1 0.8)
10 for the redshifted component and a lower limit of 0.3
10 for the blueshifted component due to the blending with the redshifted
CHOCH emission. The HDO/HO 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/HO ratio, it would mean that there is
little water reprocessing from the Class 0 to Class I protostellar stage.Comment: Accepted in A&A, 10 pages, 8 figure
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.Comment: 9 pages, 4 figures, accepted for publication in ApJL. JWST/MIRI
spectrum is available for download at https://tinyurl.com/spexodisksJWS
The clumpy structure of Eridani's debris disc revisited by ALMA
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"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
significance -- one to the east of the star and the other to the northwest. We
perform -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 or . Observations over multiple epochs
are necessary to test whether the observed features rotate around the star.Comment: 16 pages, 10 figures, accepted for publication in MNRA
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 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 months, and then started slowly fading over the next
2 years, with at least three superimposed 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 and the
mass accretion rate is M yr, which are
typical values for FUors even considering the large uncertainty in the distance
( 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.Comment: Accepted to MNRA
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 ≈ 2.9 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 ~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⊙ and the mass accretion rate is 2.5 × 10-5 M⊙ yr-1, which are typical values for FUors even considering the large uncertainty in the distance ( 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
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 to H, Pa,
Br, and lines of Ca II, O I, and Na I. The H and Br
lines were detected toward Gaia20fgx in emission in its bright state, with
additional CO lines in absorption, and the Pa line with an inverse P
Cygni profile during its fading. Based on the Br lines the accretion
rate was yr for Gaia20bwa and
yr 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.Comment: Accepted to MNRA
Photometric and spectroscopic study of the EXor-like eruptive young star Gaia19fct
Funding: This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program under grant agreement No. 716155 (SACCRED) and from the "Transient Astrophysical Objects" GINOP 2.3.2-15-2016-00033 project of the National Research, Development and Innovation Office (NKFIH), Hungary, funded by the European Union. We acknowledge support from ESA PRODEX contract No. 4000132054. Zs.N., L.K., and K.V. acknowledge the support by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. K.V. is supported by the Bolyai+ grant UNKP-22-5-ELTE-1093. This project has been supported by the K-131508 grant of the Hungarian National Research, Development and Innovation Office (NKFIH) and the Élvonal grant KKP-143986. Authors acknowledge the financial support of the Austrian-Hungarian Action Foundation (101.u13, 104.u2). L.K. acknowledges the financial support of the Hungarian National Research, Development and Innovation Office grant NKFIH PD-134784. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 101004719 (OPTICON-RadioNet Pilot).Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multifilter 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 multifilter 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 and EX Lupi–type objects, it shows more similarity with EXors in general.Publisher PDFPeer reviewe
Photometric and spectroscopic study of the EXor-like eruptive young star Gaia19fct
This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program under grant agreement No. 716155 (SACCRED) and from the "Transient Astrophysical Objects" GINOP 2.3.2-15-2016-00033 project of the National Research, Development and Innovation Office (NKFIH), Hungary, funded by the European Union. We acknowledge support from ESA PRODEX contract No. 4000132054. Zs.N., L.K., and K.V. acknowledge the support by the János Bolyai Research Scholarship of the Hungarian Academy of Sciences. K.V. is supported by the Bolyai+ grant UNKP-22-5-ELTE-1093. This project has been supported by the K-131508 grant of the Hungarian National Research, Development and Innovation Office (NKFIH) and the Élvonal grant KKP-143986. Authors acknowledge the financial support of the Austrian-Hungarian Action Foundation (101.u13, 104.u2). L.K. acknowledges the financial support of the Hungarian National Research, Development and Innovation Office grant NKFIH PD-134784. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 101004719 (OPTICON-RadioNet Pilot).Gaia19fct is one of the Gaia-alerted eruptive young stars that has undergone several brightening events. We conducted monitoring observations using multifilter 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 multifilter 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 and EX Lupi–type objects, it shows more similarity with EXors in general.Publisher PDFPeer reviewe