Astrometry in crowded fields towards the Galactic Bulge

The astrometry towards the Galactic Bulge is hampered by high stellar crowding and patchy extinction. This effect is particularly severe for optical surveys such as Gaia. In this study, we assess the consistency of proper motions (PMs) between optical (Gaia DR3) and near-infrared (VIRAC2) catalogues in comparison with PMs measured with the Hubble Space Telescope (HST) in several crowded fields towards the Galactic Bulge and in Galactic globular clusters. Assuming that the PMs are well characterised, the uncertainty-normalised PM differences between pairs of catalogues are expected to follow a normal distribution. A deviation from a normal distribution defines the inflation factor $r$. Multiplying the PM uncertainties by $r$ brings the Gaia (VIRAC2) PMs into a $1\sigma$ agreement with HST PMs. The factor $r$ has a dependence on stellar surface density and for the brightest stars in our sample (G<18), there is a strong dependence on G-band magnitude. Assuming that the HST PMs are well determined and free from systematic errors, we find that Gaia DR3 PM uncertainties are better characterised, having r<1.5, in fields under 200 Gaia DR3 sources per arcmin$^2$, and are underestimated by up to a factor of 4 in fields with more than 300 Gaia DR3 sources per arcmin$^2$. For the most crowded fields in VIRAC2, the PM uncertainties are underestimated by a factor of 1.1 up to 1.5, with a dependence on J-band magnitude. In all fields, the brighter sources have the larger $r$ value. At the faint end (G>19), $r$ is close to 1, meaning that the PMs already fully agree with the HST measurements within $1\sigma$. In the crowded fields with both catalogues in common, VIRAC2 PMs agree with HST PMs and do not need an inflation factor for their uncertainties. Given the depth and completeness of VIRAC2 in such fields, it is an ideal complement to Gaia DR3 for proper motion studies towards the Galactic Bulge.Comment: Accepted for publication in A&A. 11 pages (+6 in Appendix), 9 figures (+18 in Appendix), 4 table

The Ages of Galactic Bulge Stars with Realistic Uncertainties

Using modern isochrones with customized physics and carefully considered statistical techniques, we recompute the age distribution for a sample of 91 micro-lensed dwarfs in the Galactic bulge presented by Bensby et al. (2017) and do not produce an age distribution consistent with their results. In particular, our analysis finds that only 15 of 91 stars have ages younger than 7 Gyr, compared to their finding of 42 young stars in the same sample. While we do not find a constituency of very young stars, our results do suggest the presence of an $\sim8$ Gyr population at the highest metallicities, thus contributing to long-standing debate about the age--metallicity distribution of the Galactic bulge. We supplement this with attempts at independent age determinations from two sources of photometry, BDBS and \textit{Gaia}, but find that the imprecision of photometric measurements prevents reliable age and age uncertainty determinations. Lastly, we present age uncertainties derived using a first-order consideration of global modeling uncertainties in addition to standard observational uncertainties. The theoretical uncertainties are based on the known variance of free parameters in the 1D stellar evolution models used to generate isochrones, and when included, result in age uncertainties of $2$--$5$ Gyr for this spectroscopically well-constrained sample. These error bars, which are roughly twice as large as typical literature values, constitute realistic lower limits on the true age uncertainties.Comment: accepted to ApJ; revisions complet

Radial velocities from Gaia BP/RP spectra

The Gaia mission has provided us full astrometric solutions for over $1.5$B sources. However, only the brightest 34M of those have radial velocity measurements. As a proof of concept, this paper aims to close that gap, by obtaining radial velocity estimates from the low-resolution BP/RP spectra that Gaia now provides. These spectra are currently published for about 220M sources, with this number increasing to the full $\sim 2$B Gaia sources with Gaia Data Release 4. To obtain the radial velocity measurements, we fit Gaia BP/RP spectra with models based on a grid of synthetic spectra, with which we obtain the posterior probability on the radial velocity for each object. Our measured velocities show systematic biases that depend mainly on colours and magnitudes of stars. We correct for these effects by using external catalogues of radial velocity measurements. We present in this work a catalogue of about $6.4$M sources with our most reliable radial velocity measurements and uncertainties $<300$ km s$^{-1}$ obtained from the BP/RP spectra. About 23% of these have no previous radial velocity measurement in Gaia RVS. Furthermore, we provide an extended catalogue containing all 125M sources for which we were able to obtain radial velocity measurements. The latter catalogue, however, also contains a fraction of measurements for which the reported radial velocities and uncertainties are inaccurate. Although typical uncertainties in the catalogue are significantly higher compared to those obtained with precision spectroscopy instruments, the number of potential sources for which this method can be applied is orders of magnitude higher than any previous radial velocity catalogue. Further development of the analysis could therefore prove extremely valuable in our understanding of Galactic dynamics.Comment: 14 pages, 17 figures, submitted to A&A, comments welcom

The Blanco DECam Bulge Survey (BDBS) VIII: Chemo-kinematics in the southern Galactic bulge from 2.3 million red clump stars with Gaia DR3 proper motions

The Blanco DECam Bulge Survey (BDBS) provides near-ultraviolet to near-infrared photometry for ~250 million unique stars. By combining BDBS photometry with the latest Gaia astrometry, we characterize the chemo-dynamics of red clump stars across the BDBS footprint, using an unprecedented sample size and sky coverage. We construct a sample of ~2.3 million red clump giants in the bulge with photometric metallicities, BDBS photometric distances, and proper motions. We study the kinematics of the red clump stars as a function of sky position and metallicity, by investigating proper motion rotation curves, velocity dispersions, and proper motion correlations across the southern Galactic bulge. We find that metal-poor red clump stars exhibit lower rotation amplitudes, at ~29 km s$^{-1}$ kpc^{-1}. The peak of the angular velocity is ~39 km s^{-1} kpc^{-1} for [Fe/H] ~ -0.2 dex, exhibiting declining rotation at higher [Fe/H]. The velocity dispersion is higher for metal-poor stars, while metal-rich stars show a steeper gradient with Galactic latitude, with a maximum dispersion at low latitudes along the bulge minor axis. Only metal-rich stars ([Fe/H] >~ -0.5 dex) show clear signatures of the bar in their kinematics, while the metal-poor population exhibits isotropic motions with an axisymmetric pattern around Galactic longitude l = 0. This work reports the largest sample of bulge stars with distance, metallicity, and astrometry and shows clear kinematic differences with metallicity. The global kinematics over the bulge agrees with earlier studies. However, we see striking changes with increasing metallicity and for the first time, see kinematic differences for stars with [Fe/H]>-0.5, suggesting that the bar itself may have kinematics that depends on metallicity.Comment: 12 pages, Accepted for publication in A&

Early Prediction of Response to Tyrosine Kinase Inhibitors by Quantification of EGFR Mutations in Plasma of NSCLC Patients.

IntroductionThe potential to accurately quantify epidermal growth factor receptor (EGFR) mutations in plasma from non–small-cell lung cancer patients would enable more rapid and more frequent analyses to assess disease status; however, the utility of such analyses for clinical purposes has only recently started to explore.MethodsPlasma samples were obtained from 69 patients with EGFR-mutated tumors and 21 negative control cases. EGFR mutations in plasma were analyzed by a standardized allele-specific polymerase chain reaction (PCR) test and ultra-deep next-generation sequencing (NGS). A semiquantitative index (SQI) was derived from dilutions of known EGFR mutation copy numbers. Clinical responses were evaluated by Response Evaluation Criteria in Solid Tumors 1.1 criteria and expressed as percent tumor shrinkage.ResultsThe sensitivity and specificity of the PCR test and NGS assay in plasma versus tissue were 72% versus 100% and 74% versus 100%, respectively. Quantitative indices by the PCR test and NGS were significantly correlated (p < 0.001). EGFR testing at baseline and serially at 4 to 60 days during tyrosine kinase inhibitor therapy revealed a progressive decrease in SQI, starting from day 4, in 95% of cases. The rate of SQI decrease correlated with percent tumor shrinkage at 2 months (p < 0.0001); at 14 days, it was more than 50% in 70% of patients (rapid responders). In two patients with slow response, an early increase in the circulating levels of the T790M mutation was observed. No early T790M mutations were seen in plasma samples of rapid responders.ConclusionsQuantification of EGFR mutations from plasma with a standardized PCR test is feasible. To our knowledge, this is the first study showing a strong correlation between the EGFR SQI in the first days of treatment and clinical response with relevant implications for patient management

Mucosal Adjuvanticity and Immunogenicity of LTR72, a Novel Mutant of Escherichia coli Heat-labile Enterotoxin with Partial Knockout of ADP-ribosyltransferase Activity

Heat-labile Escherichia coli enterotoxin (LT) has the innate property of being a strong mucosal immunogen and adjuvant. In the attempt to reduce toxicity and maintain the useful immunological properties, several LT mutants have been produced. Some of these are promising mucosal adjuvants. However, so far, only those that were still toxic maintained full adjuvanticity. In this paper we describe a novel LT mutant with greatly reduced toxicity that maintains most of the adjuvanticity. The new mutant (LTR72), that contains a substitution Ala → Arg in position 72 of the A subunit, showed only 0.6% of the LT enzymatic activity, was 100,000-fold less toxic than wild-type LT in Y1 cells in vitro, and was at least 20 times less effective than wild-type LT in the rabbit ileal loop assay in vivo. At a dose of 1 μg, LTR72 exhibited a mucosal adjuvanticity, similar to that observed with wild-type LT, better than that induced by the nontoxic, enzymatically inactive LTK63 mutant, and much greater than that of the recombinant B subunit. This trend was consistent for both the amounts and kinetics of the antibody induced, and priming of antigen-specific T lymphocytes. The data suggest that the innate high adjuvanticity of LT derives from the independent contribution of the nontoxic AB complex and the enzymatic activity. LTR72 optimizes the use of both properties: the enzymatic activity for which traces are enough, and the nontoxic AB complex, the effect of which is dose dependent. In fact, in dose–response experiments in mice, 20 μg of LTR72 were a stronger mucosal adjuvant than wild-type LT. This suggests that LTR72 may be an excellent candidate to be tested in clinical trials

Blanco DECam Bulge Survey (BDBS) IV: Metallicity Distributions and Bulge Structure from 2.6 Million Red Clump Stars

We present photometric metallicity measurements for a sample of 2.6 million bulge red clump stars extracted from the Blanco DECam Bulge Survey (BDBS). Similar to previous studies, we find that the bulge exhibits a strong vertical metallicity gradient, and that at least two peaks in the metallicity distribution functions appear at b < -5. We can discern a metal-poor ([Fe/H] ~ -0.3) and metal-rich ([Fe/H] ~ +0.2) abundance distribution that each show clear systematic trends with latitude, and may be best understood by changes in the bulge's star formation/enrichment processes. Both groups exhibit asymmetric tails, and as a result we argue that the proximity of a star to either peak in [Fe/H] space is not necessarily an affirmation of group membership. The metal-poor peak shifts to lower [Fe/H] values at larger distances from the plane while the metal-rich tail truncates. Close to the plane, the metal-rich tail appears broader along the minor axis than in off-axis fields. We also posit that the bulge has two metal-poor populations -- one that belongs to the metal-poor tail of the low latitude and predominantly metal-rich group, and another belonging to the metal-poor group that dominates in the outer bulge. We detect the X-shape structure in fields with |Z| > 0.7 kpc and for stars with [Fe/H] > -0.5. Stars with [Fe/H] < -0.5 may form a spheroidal or "thick bar" distribution while those with [Fe/H] > -0.1 are strongly concentrated near the plane.Comment: 26 pages, 22 figures, accepted for publication in MNRAS; the full data table is very long so only a stub table has been provided here; the full electronic table will be provided through MNRAS upon publication, but early access to the full table will be granted upon request to the author

Two-Phase Stefan Problem as the Limit Case of Two-Phase Stefan Problem with Kinetic Condition

AbstractBoth one-dimensional two-phase Stefan problem with the thermodynamic equilibrium condition u(R(t),t)=0 and with the kinetic rule uε(Rε(t),t)=εRε′(t) at the moving boundary are considered. We prove, when ε approaches zero, Rε(t) converges to R(t) in C1+δ/2[0,T] for any finite T>0, 0<δ<1