Abstract
Statistical studies of cataloged object properties are central to astrophysics. But one cannot model those objects’ population properties without the sample’s selection function, the ...quantitative understanding of which objects could have ended up in such a catalog. As didactic introductions to this topic are scarce in the astrophysical literature, we provide one here, addressing the following questions: What is a selection function? On what arguments
q
should it depend? Over what domain must a selection function be defined? What simplifying approximations can be made? And, how is a selection function used in “modeling”? We argue that volume-complete samples, limited by the faintest objects, reflect a highly suboptimal selection function, needlessly reducing the number of bright and usually rare sample members. We illustrate these points by a worked example: github.com/gaia-unlimited/WD-selection-function, deriving the space density of white dwarfs (WDs) in the Galactic neighborhood as a function of their luminosity and color, Φ
0
(
M
G
, (
B
−
R
)) in mag
−2
pc
−3
. We construct a sample
of 10
5
presumed WDs through straightforward selection cuts on the Gaia EDR3 catalog in magnitude, color, and parallax,
q
= (
G
, (
B
−
R
),
ϖ
). We then combine a simple model for Φ
0
with this selection function’s
S
(
q
)
effective survey volume to estimate Φ
0
(
M
G
, (
B
−
R
)) precisely and robustly against the detailed choices for
S
(
q
)
. This resulting WD luminosity–color function Φ
0
(
M
G
, (
B
−
R
)) differs dramatically from the initial number density distribution in the luminosity−color plane: by orders of magnitude in density and by four magnitudes in density peak location.
Stars that Move Together Were Born Together Kamdar, Harshil; Conroy, Charlie; Ting, Yuan-Sen ...
Astrophysical journal. Letters,
10/2019, Letnik:
884, Številka:
2
Journal Article
Recenzirano
Odprti dostop
It is challenging to reliably identify stars that were born together outside of actively star-forming regions and bound stellar systems. However, conatal stars should be present throughout the ...Galaxy, and their demographics can shed light on the clustered nature of star formation and the dynamical state of the disk. In previous work we presented a set of simulations of the Galactic disk that followed the clustered formation and dynamical evolution of 4 billion individual stars over the last 5 Gyr. The simulations predict that a high fraction of comoving stars with physical and 3D velocity separation of Δr < 20 pc and Δv < 1.5 km s−1 are conatal. In this Letter, we use Gaia DR2 and LAMOST DR4 data to identify and study comoving pairs. We find that the distribution of relative velocities and separations of pairs in the data is in good agreement with the predictions from the simulation. We identify 111 comoving pairs in the solar neighborhood with reliable astrometric and spectroscopic measurements. These pairs show a strong preference for having similar metallicities when compared to random field pairs. We therefore conclude that these pairs were very likely born together. The simulations predict that conatal pairs are born in clusters that follow the overall cluster mass function and in relatively young (<1 Gyr) star clusters. Gaia will eventually deliver well-determined metallicities for the brightest stars, enabling the identification of thousands of conatal pairs due to disrupting star clusters in the solar neighborhood.
Abstract
Quasars behind the Galactic plane (GPQs) are important astrometric references and useful probes of Milky Way gas. However, the search for GPQs is difficult due to large extinctions and high ...source densities in the Galactic plane. Existing selection methods for quasars developed using high Galactic latitude (high-
b
) data cannot be applied to the Galactic plane directly because the photometric data obtained from high-
b
regions and the Galactic plane follow different probability distributions. To alleviate this data set shift problem for quasar candidate selection, we adopt a transfer-learning framework at both the data and algorithm levels. At the data level, to make a training set in which a data set shift is modeled, we synthesize quasars and galaxies behind the Galactic plane based on SDSS sources and the Galactic dust map. At the algorithm level, to reduce the effect of class imbalance, we transform the three-class classification problem for stars, galaxies, and quasars into two binary classification tasks. We apply the XGBoost algorithm to Pan-STARRS1 (PS1) and AllWISE photometry for classification and an additional cut on Gaia proper motion to remove stellar contaminants. We obtain a reliable GPQ candidate catalog with 160,946 sources located at ∣
b
∣ ≤ 20° in the PS1-AllWISE footprint. Photometric redshifts of GPQ candidates achieved with the XGBoost regression algorithm show that our selection method can identify quasars in a wide redshift range (0 <
z
≲ 5). This study extends the systematic searches for quasars to the dense stellar fields and shows the feasibility of using astronomical knowledge to improve data mining under complex conditions in the big-data era.
Context.
Understanding the intricacies behind the presence and absence of sources in an astronomical catalogue is crucial for the accurate interpretation of astronomical data. In particular, for the ...multi-dimensional
Gaia
data, filters and cuts on different parameters or measurements introduce a selection function that may unintentionally alter scientific conclusions in subtle ways.
Aims.
We aim to develop a methodology to estimate the selection function for different subsamples of stars in the
Gaia
catalogue.
Methods.
Comparing the number of stars in a given subsample to that in the overall
Gaia
catalogue provides an estimate of the subsample membership probability as a function of sky position, magnitude, and colour. The method used to make this estimate must differentiate the stochastic absence of subsample stars from selection effects. When multiplied with the overall
Gaia
catalogue selection function, this provides the total selection function of the subsample.
Results.
We present our new method for estimating the selection function by applying it to the sources in
Gaia
DR3 with heliocentric radial velocity measurements. We also compute the selection function for the stars in the Gaia-Sausage/Enceladus sample, confirming that the apparent asymmetry of its debris across the sky is merely caused by selection effects.
Conclusions.
The method we have developed estimates the selection function of the stars present in a subsample of
Gaia
data, given that the subsample is completely contained in the
Gaia
parent catalogue (for which the selection function is known). This tool is made available in a GaiaUnlimited Python package.
Context.
The detection of low-mass companions to stellar hosts is important for testing the formation scenarios of these systems. Companions at wide separations are particularly intriguing objects as ...they are easily accessible for variability studies of the rotational dynamics and cloud coverage of these brown dwarfs or planetary-mass objects.
Aims.
We aim to identify new low-mass companions to young stars using the astrometric measurements provided by the
Gaia
space mission. When possible, we use high-contrast imaging data collected with VLT/SPHERE.
Methods.
We identified companion candidates from a sample of K-type, pre-main-sequence stars in the Scorpius Centaurus association using the early version of the third data release of the
Gaia
space mission. Based on the provided positions, proper motions, and magnitudes, we identified all objects within a predefined radius, whose differential proper motions are consistent with a gravitationally bound system. As the ages of our systems are known, we derived companion masses through comparison with evolutionary tracks. For seven identified companion candidates we used additional data collected with VLT/SPHERE and VLT/NACO to assess the accuracy of the properties of the companions based on
Gaia
photometry alone.
Results.
We identify 110 comoving companions that have a companionship likelihood of more than 95%. Further color-magnitude analysis confirms their Sco-Cen membership. We identify ten especially intriguing companions that have masses in the brown dwarf regime down to 20
M
Jup
. Our high-contrast imaging data confirm both astrometry and photometric masses derived from
Gaia
alone. We discovered a new brown dwarf companion, TYC 8252-533-1 B, with a projected separation of approximately 570 au from its Sun-like primary. It is likely to be located outside the debris disk around its primary star and SED modeling of
Gaia
, SPHERE, and NACO photometry provides a companion mass of 52
−11
+17
M
Jup
.
Conclusions.
We show that the
Gaia
database can identify low-mass companions at wide separations from their host stars. For K-type Sco-Cen members,
Gaia
can detect sub-stellar objects at projected separations larger than 300 au and with a sensitivity limit beyond 1000 au and a lower mass limit down to 20
M
Jup
. A similar analysis of other star-forming regions could significantly enlarge the sample size of such objects and facilitate testing of the formation and evolution theories of planetary systems.
SN 2016gkg is a nearby SN IIb discovered shortly after explosion. Like several other Type IIb events with early-time data, SN 2016gkg displays a double-peaked light curve, with the first peak ...associated with the cooling of a low-mass extended progenitor envelope. We present unprecedented intranight-cadence multi-band photometric coverage of the first light curve peak of SN 2016gkg obtained from the Las Cumbres Observatory Global Telescope network, the Asteroid Terrestrial-impact Last Alert System, the Swift satellite, and various amateur-operated telescopes. Fitting these data to analytical shock-cooling models gives a progenitor radius of ∼40-150 with ∼2-40 × 10−2 of material in the extended envelope (depending on the model and the assumed host-galaxy extinction). Our radius estimates are broadly consistent with values derived independently (in other works) from HST imaging of the progenitor star. However, the shock-cooling model radii are on the lower end of the values indicated by pre-explosion imaging. Hydrodynamical simulations could refine the progenitor parameters deduced from the shock-cooling emission and test the analytical models.
We describe a distinct retinal disorder, autosomal-recessive bestrophinopathy (ARB), that is consequent upon biallelic mutation in
BEST1 and is associated with central visual loss, a characteristic ...retinopathy, an absent electro-oculogram light rise, and a reduced electroretinogram. Heterozygous mutations in
BEST1 have previously been found to cause the two dominantly inherited disorders, Best macular dystrophy and autosomal-dominant vitreoretinochoroidopathy. The transmembrane protein bestrophin-1, encoded by
BEST1, is located at the basolateral membrane of the retinal pigment epithelium in which it probably functions as a Cl
− channel. We sequenced
BEST1 in five families, identifying DNA variants in each of ten alleles. These encoded six different missense variants and one nonsense variant. The alleles segregated appropriately for a recessive disorder in each family. No clinical or electrophysiological abnormalities were identified in any heterozygotes. We conducted whole-cell patch-clamping of HEK293 cells transfected with bestrophin-1 to measure the Cl
− current. Two ARB missense isoforms severely reduced channel activity. However, unlike two other alleles previously associated with Best disease, cotransfection with wild-type bestrophin-1 did not impair the formation of active wild-type bestrophin-1 channels, consistent with the recessive nature of the condition. We propose that ARB is the null phenotype of bestrophin-1 in humans.
Aims. We study single and binary white dwarfs in the inner halo of the Milky Way in order to learn more about the conditions under which the population of halo stars was born, such as the initial ...mass function (IMF), the star formation history, or the binary fraction. Methods. We simulate the evolution of low-metallicity halo stars at distances up to ~3 kpc using the binary population synthesis code SeBa. We use two different white dwarf cooling models to predict the present-day luminosities of halo white dwarfs. We determine the white dwarf luminosity functions (WDLFs) for eight different halo models and compare these with the observed halo WDLF of white dwarfs in the SuperCOSMOS Sky Survey. Furthermore, we predict the properties of binary white dwarfs in the halo and determine the number of halo white dwarfs that is expected to be observed with the Gaia satellite. Results. By comparing the WDLFs, we find that a standard IMF matches the observations more accurately than a top-heavy one, but the difference with a bottom-heavy IMF is small. A burst of star formation 13 Gyr ago fits slightly better than a star formation burst 10 Gyr ago and also slightly better than continuous star formation 10−13 Gyr ago. Gaia will be the first instument to constrain the bright end of the field halo WDLF, where contributions from binary WDs are considerable. Many of these will have He cores, of which a handful have atypical surface gravities (log g < 6) and reach luminosities log (L/L⊙) > 0 in our standard model for WD cooling. These so called pre-WDs, if observed, can help us to constrain white dwarf cooling models and might teach us something about the fraction of halo stars that reside in binaries.
Systemic spread of immune activation and mediator release is required for the development of anaphylaxis in humans. We hypothesized that peripheral blood leukocyte (PBL) activation plays a key role.
...To characterize PBL genomic responses during acute anaphylaxis.
PBL samples were collected at three timepoints from six patients presenting to the Emergency Department (ED) with acute anaphylaxis and six healthy controls. Gene expression patterns were profiled on microarrays, differentially expressed genes were identified, and network analysis was employed to explore underlying mechanisms.
Patients presented with moderately severe anaphylaxis after oral aspirin (2), peanut (2), bee sting (1) and unknown cause (1). Two genes were differentially expressed in patients compared to controls at ED arrival, 67 genes at 1 hour post-arrival and 2,801 genes at 3 hours post-arrival. Network analysis demonstrated that three inflammatory modules were upregulated during anaphylaxis. Notably, these modules contained multiple hub genes, which are known to play a central role in the regulation of innate inflammatory responses. Bioinformatics analyses showed that the data were enriched for LPS-like and TNF activation signatures.
PBL genomic responses during human anaphylaxis are characterized by dynamic expression of innate inflammatory modules. Upregulation of these modules was observed in patients with different reaction triggers. Our findings indicate a role for innate immune pathways in the pathogenesis of human anaphylaxis, and the hub genes identified in this study represent logical candidates for follow-up studies.
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