Context.
Planetary nebulae (PNe) are a brief but important phase of stellar evolution. The study of Galactic PNe has historically been hampered by uncertain distances, but the parallaxes of PN ...central stars (CSPNe) measured by
Gaia
are improving the situation.
Aims. Gaia
’s Early Data Release 3 (EDR3) offers higher astrometric precision and greater completeness compared to previous releases. Taking advantage of these improvements requires that the CSPNe in the catalogue be accurately identified.
Methods.
We applied our automated technique based on the likelihood ratio method to cross-match known PNe with sources in
Gaia
EDR3, using an empirically derived position and colour distribution to score candidate matches.
Results.
We present a catalogue of over 2000 sources in
Gaia
EDR3 that our method has identified as likely CSPNe or compact nebula detections. We show how the more precise parallaxes of these sources compare to previous PN statistical distances and introduce an approach to combining them to produce tighter distance constraints. We also discuss
Gaia
’s handling of close companions and bright nebulae.
Conclusions. Gaia
is unlocking new avenues for the study of PNe. The catalogue presented here will remain valid for the upcoming
Gaia
Data Release 3 (DR3) and thus provide a valuable resource for years to come.
Context.
Accurate distance measurements are fundamental to the study of planetary nebulae (PNe) but they have long been elusive. The most accurate and model-independent distance measurements for ...galactic PNe come from the trigonometric parallaxes of their central stars, which were only available for a few tens of objects prior to the
Gaia
mission.
Aims.
The accurate identification of PN central stars in the
Gaia
source catalogues is a critical prerequisite for leveraging the unprecedented scope and precision of the trigonometric parallaxes measured by
Gaia
. Our aim is to build a complete sample of PN central star detections with minimal contamination.
Methods.
We developed and applied an automated technique based on the likelihood ratio method to match candidate central stars in
Gaia
Data Release 2 (DR2) to known PNe in the Hong Kong/AAO/Strasbourg H
α
PN catalogue, taking into account the BP – RP colours of the
Gaia
sources as well as their positional offsets from the nebula centres. These parameter distributions for both true central stars and background sources were inferred directly from the data.
Results.
We present a catalogue of over 1000
Gaia
sources that our method has automatically identified as likely PN central stars. We demonstrate how the best matches enable us to trace nebula and central star evolution and to validate existing statistical distance scales, and we discuss the prospects for further refinement of the matching based on additional data. We also compare the accuracy of our catalogue to that of previous works.
We use Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) u, g, r, i, z photometry to study Milky Way halo substructure in the area around the north Galactic cap. A simple color cut (g - r < 0.4) ...reveals the tidal stream of the Sagittarius dwarf spheroidal galaxy, as well as a number of other stellar structures in the field. Two branches (A and B) of the Sagittarius stream are clearly visible in an RGB composite image created from three magnitude slices, and there is also evidence for a still more distant wrap behind the A branch. A comparison of these data with numerical models suggests that the shape of the Galactic dark halo is close to spherical.
The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical ...infall (the Eddington limit) onto stellar-mass black holes. Their X-ray luminosities in the 0.5-10 kiloelectronvolt energy band range from 10(39) to 10(41) ergs per second. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 10(40) ergs per second), which require black hole masses of 50-100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3-30 kiloelectronvolt range of 4.9 × 10(39) ergs per second. The pulsating source is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3-10 kiloelectronvolt range of 1.8 × 10(40) ergs per second. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.
Metastasis is the leading cause of morbidity for lung cancer patients. Here we demonstrate that murine tumor propagating cells (TPCs) with the markers Sca1 and CD24 are enriched for metastatic ...potential in orthotopic transplantation assays. CD24 knockdown decreased the metastatic potential of lung cancer cell lines resembling TPCs. In lung cancer patient data sets, metastatic spread and patient survival could be stratified with a murine lung TPC gene signature. The TPC signature was enriched for genes in the Hippo signaling pathway. Knockdown of the Hippo mediators Yap1 or Taz decreased in vitro cellular migration and transplantation of metastatic disease. Furthermore, constitutively active Yap was sufficient to drive lung tumor progression in vivo. These results demonstrate functional roles for two different pathways, CD24‐dependent and Yap/Taz‐dependent pathways, in lung tumor propagation and metastasis. This study demonstrates the utility of TPCs for identifying molecules contributing to metastatic lung cancer, potentially enabling the therapeutic targeting of this devastating disease.
Synopsis
The molecular characterization of tumor‐propagating cells in mouse models of lung cancer reveals CD24+/Sca1+ and increased Yap/Taz activity as predictive for tumor metastasis.
Murine lung TPCs with the markers Sca1 and CD24 are enriched for metastatic potential in orthotopic transplantation assays.
In lung cancer patient data sets, metastatic spread and patient survival could be stratified with a murine lung TPC gene signature.
Knockdown of the Hippo mediators Yap1 or Taz decreased migration and metastatic potential of lung cancer cells.
Yap activation was sufficient for driving tumor progression in the Kras mouse model of lung cancer.
The molecular characterization of tumor‐propagating cells in mouse models of lung cancer reveals CD24+/Sca1+ and increased Yap/Taz activity as predictive for tumor metastasis.
A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na i D absorption lines, interpreted as evidence of circumstellar ...material surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass-loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the European Southern Observatory Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (∼20 per cent) of SNe Ia displaying blueshifted narrow Na i D absorption features compared to redshifted Na i D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na i D absorption and SNe Ia displaying blueshifted narrow Na i D absorption features have broader light curves. The strength of the Na i D absorption is stronger in SNe Ia displaying blueshifted Na i D absorption features than those without blueshifted features, and the strength of the blueshifted Na i D is correlated with the B − V colour of the SN at maximum light. This strongly suggests the absorbing material is local to the SN. In the context of the progenitor systems of SNe Ia, we discuss the significance of these findings and other recent observational evidence on the nature of SN Ia progenitors. We present a summary that suggests that there are at least two distinct populations of normal, cosmologically useful SNe Ia.
Tidal disruption events (TDEs) are transient flares produced when a star is ripped apart by the gravitational field of a supermassive black hole (SMBH). We have observed a transient source in the ...western nucleus of the merging galaxy pair Arp 299 that radiated >1.5 × 10
erg at infrared and radio wavelengths but was not luminous at optical or x-ray wavelengths. We interpret this as a TDE with much of its emission reradiated at infrared wavelengths by dust. Efficient reprocessing by dense gas and dust may explain the difference between theoretical predictions and observed luminosities of TDEs. The radio observations resolve an expanding and decelerating jet, probing the jet formation and evolution around a SMBH.
ABSTRACT
Ultraluminous X-ray sources (ULXs) provide a unique opportunity to probe the geometry and energetics of super-Eddington accretion. The radiative processes involved in super-Eddington ...accretion are not well understood, and so studying correlated variability between different energy bands can provide insights into the causal connection between different emitting regions. We present a spectral-timing analysis of NGC 1313 X-1 from a recent XMM–Newton campaign. The spectra can be decomposed into two thermal-like components, the hotter of which may originate from the inner accretion disc, and the cooler from an optically thick outflow. We find correlated variability between hard (2–10 keV) and soft (0.3–2 keV) bands on kilosecond time-scales, and find a soft lag of ∼150 s. The covariance spectrum suggests that emission contributing to the lags is largely associated with the hotter of the two thermal-like components, likely originating from the inner accretion flow. This is only the third ULX to exhibit soft lags. The lags range over three orders of magnitude in amplitude, but all three are ∼5–20 per cent of the corresponding characteristic variability time-scales. If these soft lags can be understood in the context of a unified picture of ULXs, then lag time-scales may provide constraints on the density and extent of radiatively driven outflows.
We present new techniques for improving the efficiency of supernova (SN) classification at high redshift using 64 candidates observed at Gemini North and South during the first year of the Supernova ...Legacy Survey (SNLS). The SNLS is an ongoing 5 year project with the goal of measuring the equation of state of dark energy by discovering and following over 700 high-redshift SNe Ia using data from the Canada-France-Hawaii Telescope Legacy Survey. We achieve an improvement in the SN Ia spectroscopic confirmation rate: at Gemini 71% of candidates are now confirmed as SNe Ia, compared to 54% using the methods of previous surveys. This is despite the comparatively high redshift of this sample, in which the median SN Ia redshift is z = 0.81 (0.155 , z , 1.01). These improvements were realized because we use the unprecedented color coverage and light curve sampling of the SNLS to predict whether a candidate is a SN Ia and to estimate its redshift, before obtaining a spectrum, using a new technique called the "SN photo-z." In addition, we have improved techniques for galaxy subtraction and SN template j super(2) fitting, allowing us to identify candidates even when they are only 15% as bright as the host galaxy. The largest impediment to SN identification is found to be host galaxy contamination of the spectrum - when the SN was at least as bright as the underlying host galaxy the target was identified more than 90% of the time. However, even SNe in bright host galaxies can be easily identified in good seeing conditions. When the image quality was better than 0.55, the candidate was identified 88% of the time. Over the 5 year course of the survey, using the selection techniques presented here, we will be able to add 6170 more confirmed SNe Ia than would be possible using previous methods.
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