Abstract
Tracing dust in small dense molecular cores is a powerful tool to study the conditions required for ices to form during the prestellar phase. To study these environments, five molecular ...cores were observed: three with ongoing low-mass star formation (B59, B335, and L483), and two starless collapsing cores (L63 and L694-2). Deep images were taken in the infrared
JHK
bands with the United Kingdom Infrared Telescope WFCAM (Wide Field Camera) instrument and IRAC channels 1 and 2 on the Spitzer Space Telescope. These five photometric bands were used to calculate extinction along the line of sight toward background stars. After smoothing the data, we produced high spatial resolution extinction maps (∼13″–29″). The maps were then projected into the third dimension using the AVIATOR algorithm implementing the inverse Abel transform. The volume densities of the total hydrogen were measured along lines of sight where ices (H
2
O, CO, and CH
3
OH) have previously been detected. We find that lines of sight with pure CH
3
OH or a mixture of CH
3
OH with CO have maximum volume densities above 1.0 × 10
5
cm
−3
. These densities are only reached within a small fraction of each of the cores (∼0.3%–2.1%). CH
3
OH presence may indicate the onset of complex organic molecule formation within dense cores, and thus we can constrain the region where this onset can begin. The maximum volume densities toward star-forming cores in our sample (∼(1.2–1.7) × 10
6
cm
−3
) are higher than those toward starless cores (∼(3.5–9.5) × 10
5
cm
−3
).
Abstract
A previously unremarkable star near the Canis Major OB1/R1 association underwent an episode of multiple deep brightness minima. Light curves based on archival Gaia, Zwicky Transient Facility ...(ZTF), and NEOWISE data and additional observations from the Las Cumbres Observatory and UKIRT show that the star was not variable prior to 2019 August 18 (MJD 58700), and on that date started showing brightness dips of up to 3 mag in the Gaia
G
and ZTF
r
bandpasses. After MJD 59500, ≈800 days after the onset of these dipping events, the star returned to its previous brightness, and no significant dipping events have been recorded since. Compared to the stable phase, NEOWISE IR photometry in the W1 and W2 bands indicates a generally redder color, and both decreases and increases in brightness at different times during the dipping episode. The spectrum of Gaia21bcv taken after the end of the dipping episode shows several neutral and ionized metal absorption lines, including Li, indicating a spectral type of ≈K5. Variable emission from O
i
was observed. The H
α
absorption in Gaia21bcv is too faint and irregular for this spectral type, indicating that the line is partly filled in by variable emission, a signature of weak episodic accretion. Gaia21bcv lies above the zero-age main sequence, but is much fainter than typical R CrB stars. We interpret the light curve of Gaia21bcv as being similar to the occultation events in
ϵ
Aurigae, i.e., occultation by a disk around a companion object orbiting the primary star.
In the episodic accretion scenario, a large fraction of the protostellar mass accretes during repeated and large bursts of accretion. Since outbursts on protostars are typically identified at ...specific wavelengths, interpreting these outbursts requires converting this change in flux to a change in total luminosity. The Class I young stellar object EC 53 in the Serpens Main cloud has undergone repeated increases in brightness at 850 m that are likely caused by bursts of accretion. In this study, we perform two- and three-dimensional continuum radiative transfer modeling to quantify the internal luminosity rise in EC 53 that corresponds to the factor of ∼1.5 enhancement in flux at 850 m. We model the spectral energy distribution and radial intensity profile in both the quiescent and outburst phases. The internal luminosity in the outburst phase is ∼3.3 times brighter than the luminosity in the quiescent phase. The radial intensity profile analysis demonstrates that the detected submillimeter flux variation of EC 53 comes from the heated envelope by the accretion burst. We also find that the role of external heating of the EC 53 envelope by the interstellar radiation field is insignificant.
The infrared young stellar outflow source MHO 3252 Y3 in the Serpens South star-forming region was found to be variable. The available photometric data can be fitted with a double-peaked light curve ...with a period of 904 days. Color variations are consistent with variable extinction with a flatter wavelength dependence than interstellar extinction, i.e., larger grains. MHO 3252 Y3 is the source of a large-scale bipolar outflow, but the most recent outflow activity has produced a microjet detectable in the shock-excited H2 1-0 S(1) line, while Fe ii emission appears confined to the immediate vicinity of the central star. The proper motion of individual shock fronts in the H2 microjet has been measured and traces these knots back to ejection events in the past two centuries. Integral field spectroscopy with the Keck 1 adaptive optics system and the OSIRIS instrument shows velocity components near the launch region that are distinct from the microjet in both radial velocity and apparent proper motion. They match the prediction of dual wind models with a distinct low-velocity disk wind component. We find evidence for the entrainment of this low-velocity component into the high-velocity microjet, leading to shock-excited emission at intermediate velocities in an envelope around the microjet.
The Outflow of The Protostar in B335. I Hodapp, Klaus W.; Chu, Laurie L.; Greene, Thomas ...
The Astronomical journal,
03/2024, Letnik:
167, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Abstract The isolated globule B335 contains a single, low-luminosity Class 0 protostar associated with a bipolar nebula and outflow system seen nearly perpendicular to its axis. We observed the ...innermost regions of this outflow as part of JWST/NIRCam Guaranteed Time Observations program 1187, primarily intended for wide-field slitless spectroscopy of background stars behind the globule. We find a system of expanding shock fronts with kinematic ages of only a few decades emerging symmetrically from the position of the embedded protostar, which is not directly detected at NIRCam wavelengths. The innermost and youngest of the shock fronts studied here shows strong emission from CO. The next older shock front shows less CO and the third shock front shows only H 2 emission in our data. This third and most distant of these inner shock fronts shows substantial evolution of its shape since it was last observed with high spatial resolution in 1996 with Keck/NIRC. This may be evidence of a faster internal shock catching up with a slower one and of the two shocks merging.
ABSTRACT The small molecular cloud Lynds 1634 contains at least three outflow sources. We found one of these, IRS 7, to be variable with a period of 37.14 0.04 days and an amplitude of approximately ...2 mag in the Ks band. The light curve consists of a quiescent phase with little or no variation, and a rapid outburst phase. During the outburst phase, the rapid variation in brightness generates light echoes that propagate into the surrounding molecular cloud, allowing a measurement of the distance to IRS 7 of 404 pc 35 pc. We observed only a marginally significant change in the H − K color during the outburst phase. The K-band spectrum of IRS 7 shows CO bandhead emission but its equivalent width does not change significantly with the phase of the light curve. The H2 1-0 S(1) line emission does not follow the variability of the continuum flux. We also used the imaging data for a proper motion study of the outflows originating from the IRS 7 and the far-infrared source IRAS 05173-0555, and confirm that these are indeed distinct outflows.
ABSTRACT We present a recalibration of the Sloan Digital Sky Survey (SDSS) photometry with new flat fields and zero points derived from Pan-STARRS1. Using point-spread function (PSF) photometry of 60 ...million stars with 16 < r < 20, we derive a model of amplifier gain and flat-field corrections with per-run rms residuals of 3 millimagnitudes (mmag) in griz bands and 15 mmag in u band. The new photometric zero points are adjusted to leave the median in the Galactic north unchanged for compatibility with previous SDSS work. We also identify transient non-photometric periods in SDSS ("contrails") based on photometric deviations co-temporal in SDSS bands. The recalibrated stellar PSF photometry of SDSS and PS1 has an rms difference of {9, 7, 7, 8} mmag in griz, respectively, when averaged over 15′ regions.
We study the outflow activity, photometric variability, and morphology of three very young stellar objects in the Serpens NW star-forming region: OO Serpentis, EC 37 (V370 Ser), and EC 53 (V371 Ser). ...High spatial resolution Keck/NIRC2 laser guide star adaptive optics images obtained in 2007 and 2009 in broadband K and in a narrowband filter centered on the 1-0 S(1) emission line of H2 allow us to identify the outflows from all three objects. We also present new, seeing-limited data on the photometric evolution of the OO Ser reflection nebula and re-analyze previously published data. We find that OO Ser declined in brightness from its outburst peak in 1995 to about 2003, but that this decline has recently stopped and actually reversed itself in some areas of the reflection nebula. The morphology and proper motions of the shock fronts MHO 2218 near EC 37 suggest that they all originate in EC 37 and that this is an outflow seen nearly along its axis. We identify an H2 jet emerging from the cometary nebula EC 53. The star illuminating EC 53 is periodically variable with a period of 543 days and has a close-by, non-variable companion at a projected distance of 92 AU. We argue that the periodic variability is the result of accretion instabilities triggered by another very close, not directly observable, binary companion and that EC 53 can be understood in the model of a multiple system developing into a hierarchical configuration.
ABSTRACT Exoplanets in their infancy are ideal targets to probe the formation and evolution history of planetary systems, including the planet migration and atmospheric evolution and dissipation. In ...this paper, we present spectroscopic observations and analyses of two planetary transits of K2-33b, which is known to be one of the youngest transiting planets (age ≈ 8–11 Myr) around a pre-main-sequence M-type star. Analysing K2-33’s near-infrared spectra obtained by the IRD instrument on Subaru, we investigate the spin-orbit angle and transit-induced excess absorption for K2-33b. We attempt both classical modelling of the Rossiter–McLaughlin (RM) effect and Doppler-shadow analyses for the measurements of the projected stellar obliquity, finding a low angle of $\lambda =-6_{-58}^{+61}$ deg (for RM analysis) and $\lambda =-10_{-24}^{+22}$ deg (for Doppler-shadow analysis). In the modelling of the RM effect, we allow the planet-to-star radius ratio to float freely to take into account the possible smaller radius in the near infrared, but the constraint we obtain ($R_p/R_s=0.037_{-0.017}^{+0.013}$) is inconclusive due to the low radial-velocity precision. Comparison spectra of K2-33 of the 1083 nm triplet of metastable ortho-He I obtained in and out of the 2021 transit reveal excess absorption that could be due to an escaping He-rich atmosphere. Under certain conditions on planet mass and stellar XUV emission, the implied escape rate is sufficient to remove an Earth-mass H/He in ∼1 Gyr, transforming this object from a Neptune to a super-Earth.
Abstract
We report observations with the JWST/NIRCam coronagraph of the Fomalhaut (
α
PsA) system. This nearby A star hosts a complex debris disk system discovered by the IRAS satellite. Observations ...in F444W and F356W filters using the round 430R mask achieve a contrast ratio of ∼4 × 10
−7
at 1″ and ∼4 × 10
−8
outside of 3″. These observations reach a sensitivity limit of <1
M
Jup
across most of the disk region. Consistent with the hypothesis that Fomalhaut b is not a massive planet but is a dust cloud from a planetesimal collision, we do not detect it in either F356W or F444W (the latter band where a Jovian-sized planet should be bright). We have reliably detected 10 sources in and around Fomalhaut and its debris disk, all but one of which are coincident with Keck or Hubble Space Telescope sources seen in earlier coronagraphic imaging; we show them to be background objects, including the “Great Dust Cloud” identified in Mid-Infrared Instrument (MIRI) data. However, one of the objects, located at the edge of the inner dust disk seen in the MIRI images, has no obvious counterpart in imaging at earlier epochs and has a relatively red F356W–F444W > 0.7 mag (Vega) color. Whether this object is a background galaxy, brown dwarf, or a Jovian-mass planet in the Fomalhaut system will be determined by an approved Cycle 2 follow-up program. Finally, we set upper limits to any scattered light from the outer ring, placing a weak limit on the dust albedo at F356W and F444W.
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