42 research outputs found
Far infrared CO and HO emission in intermediate-mass protostars
Intermediate-mass young stellar objects (YSOs) provide a link to understand
how feedback from shocks and UV radiation scales from low to high-mass star
forming regions. Aims: Our aim is to analyze excitation of CO and HO in
deeply-embedded intermediate-mass YSOs and compare with low-mass and high-mass
YSOs. Methods: Herschel/PACS spectral maps are analyzed for 6 YSOs with
bolometric luminosities of . The maps
cover spatial scales of AU in several CO and HO lines located
in the m range. Results: Rotational diagrams of CO show two
temperature components at K and
K, comparable to low- and high-mass protostars
probed at similar spatial scales. The diagrams for HO show a single
component at K, as seen in low-mass protostars, and
about K lower than in high-mass protostars. Since the uncertainties in
are of the same order as the difference between the
intermediate and high-mass protostars, we cannot conclude whether the change in
rotational temperature occurs at a specific luminosity, or whether the change
is more gradual from low- to high-mass YSOs. Conclusions: Molecular excitation
in intermediate-mass protostars is comparable to the central AU of
low-mass protostars and consistent within the uncertainties with the high-mass
protostars probed at AU scales, suggesting similar shock
conditions in all those sources.Comment: Accepted to Astronomy & Astrophysics. 4 pages, 5 figures, 3 table
Vertically extended and asymmetric CN emission in the Elias 2-27 protoplanetary disk
Elias 2-27 is a young star that hosts an extended, bright and inclined disk
of dust and gas. The inclination and extreme flaring of the disk make Elias
2-27 an ideal target to study the vertical distribution of molecules,
particularly CN. We directly trace the emission of CN in Elias 2-27 and compare
it to previously published CO isotopologue data. CN emission is
analyzed in two different transitions and , for
which we detect two hyperfine group transitions. The vertical location of CN
emission is traced directly from the channel maps, following geometrical
methods that have been previously used to analyze the CO emission of Elias
2-27. Analytical models are used to parametrize the vertical profile of each
molecule and study the extent of each tracer, additionally we compute radial
profiles of column density and optical depth. We show that the vertical
location of CN and CO isotopologues in Elias 2-27 is layered and consistent
with predictions from thermochemical models. A north/south asymmetry in the
radial extent of CN is detected and we find that the CN emission is mostly
optically thin and constrained vertically to a thin slab at 0.5. A
column density of 10\,cm is measured in the inner disk which for
the north side decreases to 10\,cm and for the south side to
10\,cm in the outer regions. In Elias 2-27, CN traces a
vertically elevated region above the midplane, very similar to that traced by
CO. The inferred CN properties are consistent with thermo-chemical disk
models, in which CN formation is initiated by the reaction of N with UV-pumped
H. The observed north/south asymmetry may be caused by either ongoing
infall or by a warped inner disk. This study highlights the importance of
tracing the vertical location of various molecules to constrain the disk
physical conditions.Comment: Accepted for publication in A&A, 19 pages, 14 figure
ALMA observations of dust polarization and molecular line emission from the Class 0 protostellar source Serpens SMM1
We present high angular resolution dust polarization and molecular line
observations carried out with the Atacama Large Millimeter/submillimeter Array
(ALMA) toward the Class 0 protostar Serpens SMM1. By complementing these
observations with new polarization observations from the Submillimeter Array
(SMA) and archival data from the Combined Array for Research in Millimeter-wave
Astronomy (CARMA) and the James Clerk Maxwell Telescopes (JCMT), we can compare
the magnetic field orientations at different spatial scales. We find major
changes in the magnetic field orientation between large (~0.1 pc) scales --
where the magnetic field is oriented E-W, perpendicular to the major axis of
the dusty filament where SMM1 is embedded -- and the intermediate and small
scales probed by CARMA (~1000 AU resolution), the SMA (~350 AU resolution), and
ALMA (~140 AU resolution). The ALMA maps reveal that the redshifted lobe of the
bipolar outflow is shaping the magnetic field in SMM1 on the southeast side of
the source; however, on the northwestern side and elsewhere in the source, low
velocity shocks may be causing the observed chaotic magnetic field pattern.
High-spatial-resolution continuum and spectral-line observations also reveal a
tight (~130 AU) protobinary system in SMM1-b, the eastern component of which is
launching an extremely high-velocity, one-sided jet visible in both CO(2-1) and
SiO(5-4); however, that jet does not appear to be shaping the magnetic field.
These observations show that with the sensitivity and resolution of ALMA, we
can now begin to understand the role that feedback (e.g., from protostellar
outflows) plays in shaping the magnetic field in very young, star-forming
sources like SMM1.Comment: 15 pages, 6 figures, 4 tables, 1 appendix. Accepted for publication
in the Astrophysical Journal. Materials accessible in the online version of
the (open-access) ApJ article include the FITS files used to make the ALMA
image in Figure 1(d), and a full, machine-readable version of Table
Vertically extended and asymmetric CN emission in the Elias 2-27 protoplanetary disk
Stars and planetary systemsInterstellar matter and star formatio
PENELLOPE V. The magnetospheric structure and the accretion variability of the classical T Tauri star HM Lup
HM Lup is a young M-type star that accretes material from a circumstellar
disk through a magnetosphere. Our aim is to study the inner disk structure of
HM Lup and to characterize its variability. We used spectroscopic data from
HST/STIS, X-Shooter, and ESPRESSO taken in the framework of the ULLYSES and
PENELLOPE programs, together with photometric data from TESS and AAVSO. The
2021 TESS light curve shows variability typical for young stellar objects of
the "accretion burster" type. The spectra cover the temporal evolution of the
main burst in the 2021 TESS light curve. We compared the strength and
morphology of emission lines from different species and ionization stages. We
determined the mass accretion rate from selected emission lines and from the UV
continuum excess emission at different epochs, and we examined its relation to
the photometric light curves. The emission lines in the optical spectrum of HM
Lup delineate a temperature stratification along the accretion flow. While the
wings of the H I and He I lines originate near the star, the lines of species
such as Na I, Mg I, Ca I, Ca II, Fe I, and Fe II are formed in an outer and
colder region. The shape and periodicity of the 2019 and 2021 TESS light
curves, when qualitatively compared to predictions from magnetohydrodynamic
models, suggest that HM Lup was in a regime of unstable ordered accretion
during the 2021 TESS observation due to an increase in the accretion rate.
Although HM Lup is not an extreme accretor, it shows enhanced emission in the
metallic species during this high accretion state that is produced by a density
enhancement in the outer part of the accretion flow.Comment: 15 pages, 14 figures. Accepted for publication in A&
Complex organic molecules in low-mass protostars on Solar System scales -- II. Nitrogen-bearing species
The chemical inventory of planets is determined by the physical and chemical
processes that govern the early phases of star formation. The aim is to
investigate N-bearing complex organic molecules towards two Class 0 protostars
(B1-c and S68N) at millimetre wavelengths with ALMA. Next, the results of the
detected N-bearing species are compared with those of O-bearing species for the
same and other sources. ALMA observations in Band 6 ( 1 mm) and Band 5
( 2 mm) are studied at 0.5" resolution, complemented by Band 3
( 3 mm) data in a 2.5" beam. NH2CHO, C2H5CN, HNCO, HN13CO, DNCO,
CH3CN, CH2DCN, and CHD2CN are identified towards the investigated sources.
Their abundances relative to CH3OH and HNCO are similar for the two sources,
with column densities that are typically an order of magnitude lower than those
of O-bearing species. The largest variations, of an order of magnitude, are
seen for NH2CHO abundance ratios with respect to HNCO and CH3OH and do not
correlate with the protostellar luminosity. In addition, within uncertainties,
the N-bearing species have similar excitation temperatures to those of
O-bearing species ( 100 300 K). The similarity of most abundances
with respect to HNCO, including those of CH2DCN and CHD2CN, hints at a shared
chemical history, especially the high D/H ratio in cold regions prior to star
formation. However, some of the variations in abundances may reflect the
sensitivity of the chemistry to local conditions such as temperature (e.g.
NH2CHO), while others may arise from differences in the emitting areas of the
molecules linked to their different binding energies in the ice. The two
sources discussed here add to the small number of sources with such a detailed
chemical analysis on Solar System scales. Future JWST data will allow a direct
comparison between the ice and gas abundances of N-bearing species.Comment: Accepted to A&A, 41 pages, 37 figure
The diverse chemistry of protoplanetary disks as revealed by JWST
Early results from the JWST-MIRI guaranteed time programs on protostars
(JOYS) and disks (MINDS) are presented. Thanks to the increased sensitivity,
spectral and spatial resolution of the MIRI spectrometer, the chemical
inventory of the planet-forming zones in disks can be investigated with
unprecedented detail across stellar mass range and age. Here data are presented
for five disks, four around low-mass stars and one around a very young
high-mass star. The mid-infrared spectra show some similarities but also
significant diversity: some sources are rich in CO2, others in H2O or C2H2. In
one disk around a very low-mass star, booming C2H2 emission provides evidence
for a ``soot'' line at which carbon grains are eroded and sublimated, leading
to a rich hydrocarbon chemistry in which even di-acetylene (C4H2) and benzene
(C6H6) are detected (Tabone et al. 2023). Together, the data point to an active
inner disk gas-phase chemistry that is closely linked to the physical structure
(temperature, snowlines, presence of cavities and dust traps) of the entire
disk and which may result in varying CO2/H2O abundances and high C/O ratios >1
in some cases. Ultimately, this diversity in disk chemistry will also be
reflected in the diversity of the chemical composition of exoplanets.Comment: 17 pages, 8 figures. Author's version of paper submitted to Faraday
Discussions January 18 2023, Accepted March 16 202
JOYS: JWST Observations of Young protoStars: Outflows and accretion in the high-mass star-forming region IRAS23385+605
Aims: The JWST program JOYS (JWST Observations of Young protoStars) aims at
characterizing the physical and chemical properties of young high- and low-mass
star-forming regions, in particular the unique mid-infrared diagnostics of the
warmer gas and solid-state components. We present early results from the
high-mass star formation region IRAS23385+6053. Methods: The JOYS program uses
the MIRI MRS with its IFU to investigate a sample of high- and low-mass
star-forming protostellar systems. Results: The 5 to 28mum MIRI spectrum of
IRAS23385+6053 shows a plethora of features. While the general spectrum is
typical for an embedded protostar, we see many atomic and molecular gas lines
boosted by the higher spectral resolution and sensitivity compared to previous
space missions. Furthermore, ice and dust absorption features are also present.
Here, we focus on the continuum emission, outflow tracers like the H2, [FeII]
and [NeII] lines as well as the potential accretion tracer Humphreys alpha
HI(7--6). The short-wavelength MIRI data resolve two continuum sources A and B,
where mid-infrared source A is associated with the main mm continuum peak. The
combination of mid-infrared and mm data reveals a young cluster in its making.
Combining the mid-infrared outflow tracer H2, [FeII] and [NeII] with mm SiO
data shows a complex interplay of at least three molecular outflows driven by
protostars in the forming cluster. Furthermore, the Humphreys alpha line is
detected at a 3-4sigma level towards the mid-infrared sources A and B.
Following Rigliaco et al. (2015), one can roughly estimate accretion
luminosities and corresponding accretion rates between ~2.6x10^-6 and
~0.9x10^-4 M_sun/yr. This is discussed in the context of the observed outflow
rates. Conclusions: The analysis of the MIRI MRS observations for this young
high-mass star-forming region reveals connected outflow and accretion
signatures.Comment: 12 pages, 9 figures, accepted for Astronomy & Astrophysics, the paper
is also available at https://www2.mpia-hd.mpg.de/homes/beuther/papers.htm
FAUST: IX. Multiband, multiscale dust study of L1527 IRS. Evidence for variations in dust properties within the envelope of a class 0/I young stellar object
Context. Early dust grain growth in protostellar envelopes infalling on young disks has been suggested in recent studies, supporting the hypothesis that dust particles start to agglomerate already during the class 0/I phase of young stellar objects. If this early evolution were confirmed, it would impact the usually assumed initial conditions of planet formation, where only particles with sizes ≲0.25 µm are usually considered for protostellar envelopes. /
Aims. We aim to determine the maximum grain size of the dust population in the envelope of the class 0/I protostar L1527 IRS, located in the Taurus star-forming region (140 pc). /
Methods. We use Atacama Large millimeter/submillimeter Array and Atacama Compact Array archival data and present new observations, in an effort to both enhance the signal-to-noise ratio of the faint extended continuum emission and properly account for the compact emission from the inner disk. Using observations performed in four wavelength bands and extending the spatial range of previous studies, we aim to place tight constraints on the spectral (α) and dust emissivity (β) indices in the envelope of L1527 IRS. /
Results. We find a rather flat α ~ 3.0 profile in the range 50–2000 au. Accounting for the envelope temperature profile, we derived values for the dust emissivity index, 0.9 < β < 1.6, and reveal a tentative, positive outward gradient. This could be interpreted as a distribution of mainly interstellar medium like grains at 2000 au, gradually progressing to (sub)millimeter-sized dust grains in the inner envelope, where at R = 300 au, β = 1.1 ± 0.1.
Our study supports a variation of the dust properties in the envelope of L1527 IRS. We discuss how this can be the result of in situ grain growth, dust differential collapse from the parent core, or upward transport of disk large grains