21 research outputs found
A study of the cold cores population in the star-forming region in Serpens
The purpose of this work is to produce the Core Mass Function (CMF)
of the Serpens star-forming region and confront it with the Initial
Mass Function (IMF), the statistical distribution of initial star mass.
As Testi & Sergent (1998) discovered, the power-law index of the slope
of the CMF is very close to the one of the Salpeter’s IMF (Salpeter,
1955): dN/dM / M2.35. This strongly suggests that the stellar IMF
results from the fragmentation process in turbulent cloud cores rather
than from stellar accretion mechanisms and gives a huge contribute to
undestanding the star formation.
For this work, we started from the data delivered by the European
satellite Herschel and produced the maps of the Serpens with Unimap
code (Piazzo et al, 2015). Hence we obtained a core catalogue with two
different softwares getsources (Men'shchikov et al, 2012) and CuTEx
(Molinari et al, 2011) and we eliminated from it any source that is
not a core.
A full discussion of the cores physical propreties as well as the
whole region is under preparation
Accretion variability of the multiple T Tauri system VW Cha
Classical T Tauri stars are low-mass objects, which are still accreting
material from the surrounding circumstellar disk. The accretion process is
essential in the formation of Sun-like stars and in setting the properties of
the disk at the time when planet formation occurs. We constructed a complex
dataset in order to examine the accretion process of VW Cha, a classical T
Tauri multiple system with the aim of studying the physical origin of the
photometric and spectroscopic variability of the system. The TESS Space
Telescope observed VW Cha between 2019 April 22 and June 19, and we
complemented these data with contemporaneous ground-based band
photometric measurements. In addition, we obtained high-resolution optical
spectra with the VLT/ESPRESSO and the 2.2\,m/FEROS instruments. Analyzing these
data, we found that the TESS light curve shows photometric variations on
timescales from minutes to weeks with a peak-to-peak amplitude of 0.8
mag. The near-infrared light curves follow the shape of the optical
measurements, however, the peak-to-peak amplitudes are slightly increasing
towards the longer wavelengths. We took spectra in both fainter and brighter
photometric states of the system, allowing us to examine the origin of a
photometric brightening event. Our results show that this brightening event can
be explained by increased accretion. In addition, our spectroscopic data also
suggest that the primary component of VW Cha is a spectroscopic binary, as it
was proposed in earlier works.Comment: Accepted for publication in ApJ. 18 pages, 10 figure
Herschel Gould Belt Survey Observations of Dense Cores in the Cepheus Flare Clouds
We present Herschel SPIRE and PACS maps of the Cepheus Flare clouds L1157, L1172, L1228, L1241, and L1251, observed by the Herschel Gould Belt Survey of nearby star-forming molecular clouds. Through modified blackbody fits to the SPIRE and PACS data, we determine typical cloud column densities of (0.5–1.0) × 1021 cm‑2 and typical cloud temperatures of 14–15 K. Using the getsources identification algorithm, we extract 832 dense cores from the SPIRE and PACS data at 160–500 μm. From placement in a mass versus size diagram, we consider 303 to be candidate prestellar cores, and 178 of these to be "robust" prestellar cores. From an independent extraction of sources at 70 μm, we consider 25 of the 832 dense cores to be protostellar. The distribution of background column densities coincident with candidate prestellar cores peaks at (2–4) × 1021 cm‑2. About half of the candidate prestellar cores in Cepheus may have formed as a result of the widespread fragmentation expected to occur within filaments of "transcritical" line mass. The lognormal robust prestellar core mass function (CMF) drawn from all five Cepheus clouds peaks at 0.56 M⊙ and has a width of ∼0.5 dex, similar to that of Aquila's CMF. Indeed, the width of Cepheus's aggregate CMF is similar to the stellar system initial mass function (IMF). The similarity of CMF widths in different clouds and the system IMF suggests a common, possibly turbulent origin for seeding the fluctuations that evolve into prestellar cores and stars
The Radial Distribution and Excitation of H2 around Young Stars in the HST-ULLYSES Survey
The spatial distribution and evolution of gas in the inner 10 au of
protoplanetary disks form the basis for estimating the initial conditions of
planet formation. Among the most important constraints derived from
spectroscopic observations of the inner disk are the radial distributions of
the major gas phase constituents, how the properties of the gas change with
inner disk dust evolution, and how chemical abundances and excitation
conditions are influenced by the high-energy radiation from the central star.
We present a survey of the radial distribution, excitation, and evolution of
inner disk molecular hydrogen (H) obtained as part of the /ULLYSES
program. We analyze far-ultraviolet spectroscopy of 71 (63 accreting) pre-main
sequence systems in the ULLYSES DR5 release to characterize the H
emission lines, H dissociation continuum emission, and major
photochemical/disk evolution driving UV emissions (Ly, UV continuum,
and C IV). We use the widths of the H emission lines to show that most
fluorescent H arises between 0.1 - 1.4 au from the parent star, and show
positive correlations of the average emitting radius with the accretion
luminosity and with the dust disk mass. We find a strong correlation between
H dissociation emission and both the accretion-dominated Ly
luminosity and the inner disk dust clearing, painting a picture where water
molecules in the inner 3 au are exposed to and dissociated by strong Ly
emission as the opacity of the inner disk declines with time.Comment: 19 pages, 11 figures. Accepted to the Astronomical Journa
KMOS study of the mass accretion rate from Class I to Class II in NGC 1333
Context. The mass accretion rate (\Mdot;acc) is the fundamental parameter to understand the process of mass assembly that results in the formation of a low-mass star. This parameter has been largely studied in Classical T Tauri stars in star-forming regions with ages of ∼1 − 10 Myr. However, little is known about the accretion properties of young stellar objects (YSOs) in younger regions and early stages of star formation, such as in the Class 0/I phases. Aims: We present new near-infrared spectra of 17 Class I/Flat and 35 Class II sources located in the young ( Methods: For the Class II sources in our sample, we measured the stellar parameters (SpT, AV, and L⋆) through a comparison of the IR spectra with a grid of non-accreting Class III stellar templates. We then computed the accretion luminosity by using the known correlation between Lacc and the luminosity of HI lines (Paβ and Brγ). For the Class I sample, where the presence of a large IR excess makes it impossible to use the same spectral typing method, we applied a procedure that allowed us to measure the stellar and accretion luminosity in a self-consistent way. Mass accretion rates \Mdot;acc were then measured once masses and radii were estimated adopting suitable evolutionary tracks. Results: The NGC 1333 Class II sources of our sample have Lacc ∼ 10−4 − 1 L⊙ and \Mdot;acc ∼ 10−11 − 10−7 M⊙ yr−1. We find a correlation between accretion and stellar luminosity in the form of log Lacc = (1.5 ± 0.2)log L⋆ + ( − 1.0 ± 0.1), and a correlation between the mass accretion rate and stellar mass in the form of log \Mdot;acc = (2.6 ± 0.9) log M⋆ + (−7.3 ± 0.7). Both correlations are compatible within the errors with the older Lupus star-forming region, while only the latter is consistent with results from Chamaeleon I. The Class I sample shows larger accretion luminosities (∼10−2 − 102 L⊙) and mass accretion rates (∼10−9 − 10−6 M⊙ yr−1) with respect to the Class II stars of the same cloud. However, the derived mass accretion rates are not sufficiently high to build up the inferred stellar masses, assuming steady accretion during the Class I lifetime. This suggests that the sources are not in their main accretion phase and that most of their mass has already been accumulated during a previous stage and/or that the accretion is an episodic phenomenon. We show that some of the targets originally classified as Class I through Spitzer photometry are in fact evolved or low accreting objects. This evidence can have implications for the estimated protostellar phase lifetimes. Conclusions: The accretion rates of our sample are larger in more embedded and early stage YSOs. Further observations of larger samples in young star-forming regions are needed to determine if this is a general result. In addition, we highlight the importance of spectroscopic surveys of YSOs to confirm their classification and perform a more correct estimate of their lifetime. Reduced spectra of the sources described in Tables 1 and C.1 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/650/A43 Based on observations collected at the European Southern Observatory under ESO programme 0102.C-0679A
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
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