Rapid rotation is a fundamental characteristic of classical Be stars and a crucial property allowing for the formation of their circumstellar disks. Past evolution in a mass and angular momentum ...transferring binary system offers a plausible solution to how Be stars attained their fast rotation. Although the subdwarf remnants of mass donors in such systems should exist in abundance, only a few have been confirmed due to tight observational constraints. An indirect method of detecting otherwise hidden companions is offered by their effect on the outer parts of Be star disks, which are expected to be disrupted or truncated. In the context of the infrared and radio continuum excess radiation originating in the disk, the disk truncation can be revealed by a turndown in the spectral energy distribution due to reduced radio flux levels. In this work, we search for signs of spectral turndown in a sample of 57 classical Be stars with radio data, which include new data for 23 stars and the longest-wavelength detections so far (λ 10 cm) for two stars. We confidently detect the turndown for all 26 stars with sufficient data coverage (20 of which are not known to have close binary companions). For the remaining 31 stars, the data are inconclusive as to whether the turndown is present or not. The analysis suggests that many if not all Be stars have close companions influencing their outer disks. If confirmed to be subdwarf companions, the mass transfer spin-up scenario might explain the existence of the vast majority of classical Be stars.
Abstract
We present the first results from the Transiting Exoplanet Survey Satellite (TESS) on the rotational and pulsational variability of magnetic chemically peculiar A-type stars. We analyse TESS ...2-min cadence data from sectors 1 and 2 on a sample of 83 stars. Five new rapidly oscillating Ap (roAp) stars are announced. One of these pulsates with periods around 4.7 min, making it the shortest period roAp star known to date. Four out of the five new roAp stars are multiperiodic. Three of these and the singly periodic one show the presence of rotational mode splitting. Individual frequencies are provided in all cases. In addition, seven previously known roAp stars are analysed. Additional modes of oscillation are found in some stars, while in others we are able to distinguish the true pulsations from possible aliases present in the ground-based data. We find that the pulsation amplitude in the TESS filter is typically a factor of 6 smaller than that in the B filter, which is usually used for ground-based observations. For four roAp stars we set constraints on the inclination angle and magnetic obliquity, through the application of the oblique pulsator model. We also confirm the absence of roAp-type pulsations down to amplitude limits of 6 and 13 $\mu$mag, respectively, in two of the best characterized non-oscillating Ap (noAp) stars. We announce 27 new rotational variables along with their rotation periods, and provide different rotation periods for seven other stars. Finally, we discuss how these results challenge state-of-the-art pulsation models for roAp stars.
We present a detailed description of the special procedures for calibration and quality assurance of Atacama Large Millimeter/submillimeter Array (ALMA) observations in Very Long Baseline ...Interferometry (VLBI) mode. These procedures are required to turn the phased ALMA array into a fully calibrated VLBI station. As an illustration of these methodologies, we present full-polarization observations carried out with ALMA as a phased array at 3 mm (Band 3) and 1.3 mm (Band 6) as part of Cycle-4. These are the first VLBI science observations conducted with ALMA and were obtained during a 2017 VLBI campaign in concert with other telescopes worldwide as part of the Global mm-VLBI Array (GMVA, April 1-3) and the Event Horizon Telescope (EHT, April 5-11) in ALMA Bands 3 and 6, respectively.
Abstract
We report the detection of 15 GHz radio continuum emission associated with the classical Cepheid variable star
δ
Cephei (
δ
Cep) based on observations with the Karl G. Jansky Very Large ...Array. Our results constitute the first probable detection of radio continuum emission from a classical Cepheid. We observed the star at pulsation phase
ϕ
≈ 0.43 (corresponding to the phase of maximum radius and minimum temperature) during three pulsation cycles in late 2018 and detected statistically significant emission (>5
σ
) during one of the three epochs. The observed radio emission appears to be variable at a ≳10% level on timescales of days to weeks. We also present an upper limit on the 10 GHz flux density at pulsation phase
ϕ
= 0.31 from an observation in 2014. We discuss possible mechanisms that may produce the observed 15 GHz emission, but cannot make a conclusive identification from the present data. The emission does not appear to be consistent with originating from a close-in, late-type dwarf companion, although this scenario cannot yet be strictly excluded. Previous X-ray observations have shown that
δ
Cep undergoes periodic increases in X-ray flux during pulsation phase
ϕ
≈ 0.43. The lack of radio detection in two out of three observing epochs at
ϕ
≈ 0.43 suggests that either the radio emission is not linked with a particular pulsation phase, or else that the strength of the generated radio emission in each pulsation cycle is variable.
The collection and dissemination of vertebrate ichnological data is struggling to keep up with techniques that are becoming commonplace in the wider palaeontological field. A standard protocol is ...required to ensure that data is recorded, presented and archived in a manner that will be useful both to contemporary researchers, and to future generations. Primarily, our aim is to make the 3D capture of ichnological data standard practice, and to provide guidance on how such 3D data can be communicated effectively (both via the literature and other means) and archived openly and in perpetuity. We recommend capture of 3D data, and the presentation of said data in the form of photographs, false‐colour images, and interpretive drawings. Raw data (3D models of traces) should always be provided in a form usable by other researchers (i.e. in an open format). If adopted by the field as a whole, the result will be a more robust and uniform literature, supplemented by unparalleled availability of datasets for future workers.
Abstract
We present panchromatic observations and modeling of supernova (SN) 2020tlf, the first normal Type II-P/L SN with confirmed precursor emission, as detected by the Young Supernova Experiment ...transient survey. Pre-SN activity was detected in
riz
-bands at −130 days and persisted at relatively constant flux until first light. Soon after discovery, “flash” spectroscopy of SN 2020tlf revealed narrow, symmetric emission lines that resulted from the photoionization of circumstellar material (CSM) shed in progenitor mass-loss episodes before explosion. Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a red supergiant (RSG) progenitor with zero-age main-sequence mass of only 10–12
M
⊙
, as inferred from nebular spectra. Modeling of the light curve and multi-epoch spectra with the non-LTE radiative-transfer code CMFGEN and radiation-hydrodynamical code HERACLES suggests a dense CSM limited to
r
≈ 10
15
cm, and mass-loss rate of 10
−2
M
⊙
yr
−1
. The luminous light-curve plateau and persistent blue excess indicates an extended progenitor, compatible with an RSG model with
R
⋆
= 1100
R
⊙
. Limits on the shock-powered X-ray and radio luminosity are consistent with model conclusions and suggest a CSM density of
ρ
< 2 × 10
−16
g cm
−3
for distances from the progenitor star of
r
≈ 5 × 10
15
cm, as well as a mass-loss rate of
M
̇
<
1.3
×
10
−
5
M
☉
yr
−
1
at larger distances. A promising power source for the observed precursor emission is the ejection of stellar material following energy disposition into the stellar envelope as a result of gravity waves emitted during either neon/oxygen burning or a nuclear flash from silicon combustion.
Observations with the Karl G. Jansky Very Large Array at 46 GHz (λ 7 mm) have been used to measure the size and shape of the radio photospheres of four long-period variable stars: R Leonis (R Leo), ...IRC+10216 (CW Leonis), χ Cygni (χ Cyg), and W Hydrae (W Hya). The shapes of the stars range from nearly round to ellipticities of ∼0.15. Comparisons with observations taken several years earlier show that the photospheric parameters (mean diameter, shape, and/or flux density) of each of the stars have changed over time. Evidence for brightness asymmetries and nonuniformities across the radio surfaces is also seen in the visibility domain and in images obtained using a sparse-modeling image reconstruction technique. These trends may be explained as manifestations of large-scale irregular convective flows on the stellar surface, although effects from nonradial pulsations cannot be excluded. Our data also allow a new evaluation of the proper motion of IRC+10216. Our measurement is in agreement with previous values obtained from radio-wavelength measurements, and we find no evidence of statistically significant astrometric perturbations from a binary companion.
Abstract
We present spatially resolved observations of Betelgeuse (
α
Orionis) obtained with the Karl G. Jansky Very Large Array at
λ
∼ 7 mm (44 GHz) and
λ
∼ 1.3 cm (22 GHz) on 2019 August 2, just ...prior to the onset of the historical optical dimming that occurred between late 2019 and early 2020. Our measurements suggest recent changes in the temperature and density structure of the atmosphere between radii
r
∼ 2
R
⋆ and 3
R
⋆. At
λ
7 mm the star is ∼20% dimmer than in previously published observing epochs between 1996 and 2004. We measure a mean gas temperature of
T
B
= 2270 ± 260 K at
r
∼ 2.1
R
⋆, where
R
⋆
is the canonical photospheric radius. This is ∼2
σ
lower than previously reported temperatures at comparable radii and >1200 K lower than predicted by previous semiempirical models of the atmosphere. The measured brightness temperature at
r
∼ 2.6
R
⋆
(
T
B
= 2580 ± 260 K) is also cooler than expected based on trends in past measurements. The stellar brightness profile in our current measurements appears relatively smooth and symmetric, with no obvious signatures of giant convective cells or other surface features. However, the azimuthally averaged brightness profile is found to be more complex than a uniform elliptical disk. Our observations were obtained approximately 6 weeks before spectroscopic measurements in the ultraviolet revealed evidence of increases in the chromospheric electron density in the southern hemisphere of Betelgeuse, coupled with a large-scale outflow. We discuss possible scenarios linking these events with the observed radio properties of the star, including the passage of a strong shock wave.
High-grade serous ovarian cancers have low survival rates because of their late presentation with extensive peritoneal metastases and frequent chemoresistance1, and require newtreatmentsguided by ...novel insights into pathogenesis. Here we describe the intrinsic tumour-suppressive activities ofinterferon-s (IFNs). IFNs is constitutively expressed in epithelial cells ofthe fallopian tube, the cell of origin of high-grade serous ovarian cancers, and is then lost during development ofthese tumours. We characterize its anti-tumour activity in several preclinical models: ovarian cancer patient-derived xenografts, orthotopic and disseminated syngeneic models, and tumour cell lines with or without mutations in Trp53 and Brea genes. We use manipulation ofthe IFNs receptor 1FNAR1 in different cell compartments, differential exposure status to IFNs andglobal measures of IFN signallingto showthat the mechanism ofthe anti-tumour activity of IFNs involves direct action on tumour cells and, crucially, activation of anti-tumour immunity. IFNs activated anti-tumour T and natural killer cells and prevented the accumulation and activation of myeloidderived suppressor cells and regulatory T cells. Thus, we demonstrate that IFNs is an intrinsictumour suppressor in the female reproductive tract whose activities in models of established and advanced ovarian cancer, distinct from othertype 1 IFNs, are compelling indications of potential new therapeutic approaches for ovarian cancer.
Context. High-mass star formation remains poorly understood due to observational difficulties (e.g. high dust extinction and large distances) hindering the resolution of disk-accretion and ...outflow-launching regions. Aims. Orion Source I is the closest known massive young stellar object (YSO) and exceptionally powers vibrationally-excited SiO masers at radii within 100 AU, providing a unique probe of gas dynamics and energetics. We seek to observe and image these masers with Very Long Baseline Interferometry (VLBI). Methods. We present the first images of the 28SiO v = 1, J = 2−1 maser emission around Orion Source I observed at 86 GHz (λ3 mm) with the Very Long Baseline Array (VLBA). These images have high spatial (~0.3 mas) and spectral (~0.054 km s-1) resolutions. Results. We find that the λ3 mm masers lie in an X-shaped locus consisting of four arms, with blue-shifted emission in the south and east arms and red-shifted emission in the north and west arms. Comparisons with previous images of the 28SiO v = 1,2, J = 1−0 transitions at λ7 mm (observed in 2001–2002) show that the bulk of the J = 2−1 transition emission follows the streamlines of the J = 1−0 emission and exhibits an overall velocity gradient consistent with the gradient at λ7 mm. While there is spatial overlap between the λ3 mm and λ7 mm transitions, the λ3 mm emission, on average, lies at larger projected distances from Source I (~44 AU compared with ~35 AU for λ7 mm). The spatial overlap between the v = 1, J = 1−0 and J = 2−1 transitions is suggestive of a range of temperatures and densities where physical conditions are favorable for both transitions of a same vibrational state. However, the observed spatial offset between the bulk of emission at λ3 mm and λ7 mm possibly indicates different ranges of temperatures and densities for optimal excitation of the masers. We discuss different maser pumping models that may explain the observed offset. Conclusions. We interpret the λ3 mm and λ7 mm masers as being part of a single wide-angle outflow arising from the surface of an edge-on disk rotating about a northeast-southwest axis, with a continuous velocity gradient indicative of differential rotation consistent with a Keplerian profile in a high-mass proto-binary.
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