Outburst and Splitting of Interstellar Comet 2I/Borisov

<p>We present Hubble Space Telescope observations of a photometric outburst and splitting event in interstellar comet 2I/Borisov.   The outburst, first reported with the comet outbound at 2.8 AU (Drahus et al.~2020), was caused by the expulsion of solid particles having a combined cross-section about 100 sq. km and a mass in 0.1 mm sized particles  2e7 kg.  The latter corresponds to 1e-4 of the mass of the nucleus, taken as a sphere of radius 500 m.  A transient  double nucleus was observed on UT 2020 March 30 (about three weeks after the outburst), having a cross-section 0.6 sq. km and corresponding dust mass 1e5 kg.  The secondary was absent in images taken on and before March 28, and in images taken on and after April 03.  The unexpectedly delayed appearance and rapid disappearance of the secondary are consistent with an origin through rotational bursting of one or more large (meter-sized) boulders under the action of outgassing torques, following their ejection from the main nucleus.  Overall, our observations  reveal that the outburst and splitting of the nucleus are minor events involving a negligible fraction of the total mass: 2I/Borisov will survive its passage through the planetary region largely unscathed.</p> <p>Journal: The Astrophysical Journal Letters, Volume 896, Issue 2, id.L39</p> <p> </p>

Ultradiffuse galaxies in the IC 1459 group from the VEGAS survey

ABSTRACT Using deep g, r, i imaging from the VST Early-type GAlaxy Survey (VEGAS), we have searched for ultradiffuse galaxies (UDGs) in the IC 1459 group. Assuming they are group members, we identify nine galaxies with physical sizes and surface brightnesses that match the UDG criteria within our measurement uncertainties. They have mean colours of g − i = 0.6 and stellar masses of ∼108 M⊙. Several galaxies appear to have associated systems of compact objects, e.g. globular clusters. Two UDGs contain a central bright nucleus, with a third UDG revealing a remarkable double nucleus. This appears to be the first reported detection of a double nucleus in a UDG – its origin is currently unclear.

Analysis of Related Factors of Malignant Clone Burden of Patients with Myelodysplastic Syndromes

Abstract 4979 Objective To investigate the related factors of the malignant clone burden of patients with Myelodysplastic syndromes (MDS), and explore the risk factors of cytogenetic evolution of MDS. Methods Seventy-three cases of MDS patients were enrolled in this study who received treatment in the hematological department of General Hospital of Tianjin Medical University from 2004 to 2009. Statistics methods such as t-test, Chi-square test and Logistic regression analysis were used to investigate the correlation between the malignant clone burden and its related factors such as bone marrow dysplasia, peripheral blood and iron metabolism indexes. Furthermore, the risk factors of cytogenetic evolution of MDS were also analyzed. Results Odd number-nucleus erythrocytes, double-nucleus granulocytes, hypolobated neutrophils were significantly correlated to high malignant clone burden (P<0.05). PAS positive patients and patients with dysplasia in three myeloid lineages, blasts in peripheral blood exhibited significantly higher malignant clone burden (P<0.05). Patients with abnormal karyotype presented significantly higher level of serum ferritin and lower level of unsaturated iron binding capacity (UIBC) than those with normal karyotype (P<0.05). Odd number-nucleus erythrocytes, megaloblastic granulocytes and high myeloid differentiation index (DI) are risk factors indicating cytogenetic evolution of MDS patients. Conclusion The indexes of high malignant clone burden of MDS include: odd number-nucleus erythrocytes, double-nucleus granulocytes, hypolobated neutrophils, dysplasia in three myeloid lineages, blasts in peripheral blood, positive PAS, high level of serum ferritin and low level of UIBC. The risk factors of cytogenetic evolution of MDS include: odd number-nucleus erythrocytes, megaloblastic granulocytes and high myeloid DI. Disclosures: No relevant conflicts of interest to declare.