Searching for new globular clusters in M 31 with Gaia EDR3

We found 50 new globular cluster (GC) candidates around M\,31 with Gaia Early Data Release 3 (EDR3), with the help from Pan-STARRS1 DR1 magnitudes and Pan-Andromeda Archaeological Survey (PAndAS) images. Based on the latest Revised Bologna Catalog and \textit{simbad}, we trained 2 Random Forest (RF) classifiers, the first one to distinguish extended sources from point sources and the second one to further select GCs from extended sources. From 1.85 million sources of $16^m{<}g{<}19.5^m$ and within a large area of $\sim$392\,deg$^2$ around M\,31, we selected 20,658 extended sources and 1,934 initial GC candidates. After visual inspection of the PAndAS images to eliminate the contamination of non-cluster sources, particularly galaxies, we finally got 50 candidates. These candidates are divided into 3 types (\textbf{a}, \textbf{b}, \textbf{c}) according to their projected distance $D$ to the center of M\,31 and their probability to be a true GC, $P_{GC}$, which is calculated by our second RF classifier. Among these candidates, 14 are found to be associated (in projection) with the large-scale structures within the halo of M\,31. We also provided several simple parameter criteria for selecting extended sources effectively from the Gaia EDR3, which can reach a completeness of 92.1\% with a contamination fraction lower than 10\%

Internal Calibration of LAMOST and Gaia DR3 GSP-Spec Stellar Abundances

Stellar chemical abundances are crucial and fundamental in astrophysics. However, they could suffer from substantial systematic errors according to several investigations but still lack calibrations in bulk. By using Gaia wide binaries, we find the temperature-dependent bias between the two binary components for [Fe/H] and [ α /Fe] measurements from the LAMOST low-resolution spectra and Gaia RVS spectra. At T _eff = 4000 K, the LAMOST [Fe/H] is significantly underestimated by approximately 0.4 dex when compared with its typical uncertainty of 0.1 dex. Its [ α /Fe] is overestimated by about 0.2 dex. For Gaia, the underestimation of [M/H] and overestimation of [ α /Fe] becomes pronounced near 7000 K with smaller magnitudes. We perform an internal calibration by minimizing the differences between the binary components and provide the correction curves. After corrections, the standard deviations of the residuals compared to the PASTEL catalog decrease from about 0.045/0.1 to 0.02/0.043 for LAMOST and Gaia, respectively. The chemical homogeneity of the open cluster M 44 is also improved by a factor of two. We stress that the underestimation of [Fe/H] could lead to an overestimation of binary fractions when selecting binary stars by the excess of luminosity. The method of this work could be applied to other data sets in the future. Our results will benefit statistic studies that use LAMOST and Gaia samples with a wide temperature range

Throughput Improvement by Joint Relay Selection and Link Scheduling in Relay-Assisted Cellular Networks

We consider joint relay selection and link scheduling to maximize the network throughput in relay-assisted cellular networks. The spatial reuse is leveraged by scheduling multiple links to simultaneously transmit. The coupling among relay selection, link scheduling, and the interference that is introduced by simultaneous transmissions makes this problem hard to solve. We summarize spatial reuse into two forms. The first form of spatial reuse exists among second-hop links, where relay stations transmit to mobile users. The second form of spatial reuse exists between second- and first-hop links, where the base station transmits to relay stations or mobile users. A framework is proposed to de-couple the joint problem into the following two subproblems: 1) a frame segmentation problem and 2) a relay selection problem. Under this framework, we propose two algorithms for either only the first form of spatial reuse exists or both forms of spatial reuse exist. Numerical results show that, with the first form of spatial reuse, the performance of the proposed heuristic relay selection algorithm is very close to the optimum. In the given scenario, when both forms of spatial reuse exist and the proposed heuristic frame segmentation algorithm is applied, the throughput is improved by up to more than 50% compared with the case without spatial reuse

The Dusty Red Supergiant Progenitor and the Local Environment of the Type II SN 2023ixf in M101

As one of the closest supernovae (SNe) in the last decade, SN 2023ixf is an unprecedented target to investigate the progenitor star that exploded. However, there is still significant uncertainty in the reported progenitor properties. In this work, we present a detailed study of SN 2023ixf’s progenitor with two independent analyses. We first modeled its spectral energy distribution (SED) based on Hubble Space Telescope optical, Spitzer mid-infrared (IR), and ground-based near-IR data. We find that stellar pulsation and circumstellar extinction have great impacts on SED fitting, and the result suggests a relatively massive red supergiant surrounded by C-rich dust with an initial mass of 16.2–17.4 M _⊙ . The corresponding rate of mass loss occurring at least 3 yr before the SN explosion is about 2 × 10 ^−4 M _⊙ yr ^−1 . We also derived the star formation history of the SN environment based on resolved stellar populations, and the most recent star-forming epoch corresponds to a progenitor initial mass of 17–19 M _⊙ , in agreement with that from our SED fitting. Therefore, we conclude that the progenitor of SN 2023ixf is close to the high-mass end for Type II SN progenitors

A Comprehensive Correction of the Gaia DR3 XP Spectra

By combining spectra from the CALSPEC and NGSL, as well as spectroscopic data from the LAMOST Data Release 7 (DR7), we have analyzed and corrected the systematic errors of the Gaia DR3 BP/RP (XP) spectra. The errors depend on the normalized spectral energy distribution (simplified by two independent “colors”) and G magnitude. Our corrections are applicable in the range of approximately −0.5 < BP − RP < 2, 3 < G < 17.5, and E ( B − V ) < 0.8. To validate our correction, we conduct independent tests by comparisons with the MILES and LEMONY spectra. The results demonstrate that the systematic errors of BP − RP and G have been effectively corrected, especially in the near-ultraviolet. The consistency between the corrected Gaia XP spectra and the MILES and LEMONY is better than 2% in the wavelength range of 336–400 nm and 1% in redder wavelengths. A global absolute calibration is also carried out by comparing the synthetic Gaia photometry from the corrected XP spectra with the corrected Gaia DR3 photometry. Our study opens up new possibilities for using XP spectra in many fields. A Python package is publicly available to do the corrections (doi: https://doi.org/10.12149/101375 or https://github.com/HiromonGON/GaiaXPcorrection )

Phosphorylation of Mutationally Introduced Tyrosine in the Activation Loop of HER2 Confers Gain-of-Function Activity

<div><p>Amplification, overexpression, and somatic mutation of the HER2 gene have been reported to play a critical role in tumorigenesis of various cancers. The HER2 H878Y mutation was recently reported in 11% of hepatocellular carcinoma (HCC) patients. However, its functional impact on the HER2 protein and its role in tumorigenesis has not been determined. Here, we show that HER2 H878Y is a gain-of-function mutation. Y878 represents a phosphorylation site, and phospho-Y878 interacts with R898 residue to stabilize the active conformation of HER2, thereby enhancing its kinase activity. H878Y mutant is transforming and the transformed cells are sensitive to HER2 kinase inhibitors. Thus, our study reveals the following novel mechanism underlying the tumorigenic function of the HER2 H878Y mutation: the introduction of a tyrosine residue into the kinase activation loop via mutagenesis modulates the conformation of the kinase, thereby enhancing its activity.</p></div

HKI-272 inhibits H878Y HER2 mutant elicited signaling.

<p>(A) WT and H878Y transformed Ba/f3 and parental cells were treated with 50nM of various HER2 inhibitors for 3 days to determine the viability. (B) WT and H878Y transformed Ba/f3 cells were treated with 50 or 200nM HKI-272 for 24 hours to determine HER2 phosphorylation and cleaved PARP. Western blot were carried out with antibody indicated. (C) HKI-272 efficiently eliminated soft-agar colonies of WT and H878Y transfected NIH-3T3, Beas-2B, and AML12 cells in the presence of 500nM HKI-272. (D) H878Y elicited signals are sensitive to HKI-272 inhibition. Control vector, WT and H878Y constructs transfected NIH-3T3, Beas-2B, and AML12 cells were treated with 500 nM HKI-272 for 1 hour and then subjected to Western blot analysis with antibodies indicated. # p<0.001.</p