M17 MIR: A Massive Protostar with Multiple Accretion Outbursts *

We report the discovery of a massive protostar M17 MIR embedded in a hot molecular core in M17. The multiwavelength data obtained during 1993–2019 show significant mid-IR (MIR) variations, which can be split into three stages: the decreasing phase during 1993.03–mid-2004, the quiescent phase from mid-2004 to mid-2010, and the rebrightening phase from mid-2010 until now. The variation of the 22 GHz H2O maser emission, together with the MIR variation, indicates an enhanced disk accretion rate onto M17 MIR during the decreasing and rebrightening phases. Radiative transfer modeling of the spectral energy distributions of M17 MIR in the 2005 epoch (quiescent) and 2017 epoch (accretion outburst) constrains the basic stellar parameters of M17 MIR, which is an intermediate-mass protostar (M * ∼ 5.4 M ⊙) with M ̇ acc ∼ 1.1 × 10 − 5 M ⊙ yr − 1 in the 2005 epoch and M ̇ acc ∼ 1.7 × 10 − 3 M ⊙ yr − 1 in the 2017 epoch. The enhanced M ̇ acc during outburst induces the luminosity outburst ΔL ≈ 7600 L ⊙. In the accretion outburst, a larger stellar radius is required to produce M ̇ acc consistent with the value estimated from the kinematics of H2O masers. M17 MIR shows two accretion outbursts (Δt ∼ 9–20 yr) with outburst magnitudes of about 2 mag, separated by a 6 yr quiescent phase. The accretion outburst occupies 83% of the time over 26 yr. The accretion rate in outburst is variable with amplitude much lower than the contrast between quiescent and outburst phases. The extreme youth of M17 MIR suggests that minor accretion bursts are frequent in the earliest stages of massive star formation.

Recent surge of the South Rimo Glacier, Karakoram: Dynamics Characterization using SAR data

<p>Glacier surging is an unique dynamic pattern that involves a long term quiescent phase and a sudden surge phase. The surge causes abnormal glacier movement, such as high flow velocity, transportation of large amount of ice mass, and dramatic thickening and advancing of the glacier terminus. Glacier surge not only confound the understanding of regional glacier dynamics, but also pose threats to local residents by invoking glacier lake outburst floods. </p><p>In this work, we reported the recent surge event of the South Rimo Glacier, one of the largest glaciers in Karakorum. The surge happened between 2018-2020 with very little terminus advancement, and thus it is difficult to interpret the dynamics of the event simply by visual inspections of satellite images. We studied both the topography evolution and the surface velocity change of the glacier before and during the surge. By differencing a series of digital elevation models (DEMs) produced from the TanDEM-x CoSSC data acquired between 2011 and 2017, we found that the South Rimo glacier started accumulating height in the middle stream since 2013. A bulge was built in the reservoir region since 2014 and reached its maximum height (27.51m higher than 2011) before the surge activation in 2017. Velocity maps between 2016-2020 were obtained from SAR offset tracking using Sentinel-1 images. It was shown that the surface velocity greatly increased in 2017 at areas around the bulge. The peak velocity was found in the mid of 2019 at about 10 m/day, which is of three magnitude higher than the velocity during the quiescent phase. Our work characterized the development of the recent surge of the South Rimo Glacier, and highlighted the value of high resolution DEM products and velocity maps in pre-identifying glacier surge and mitigating related hazards.</p>

The Effects of IL-2 Concentration and Adding Manner on Proliferation and Function of CIKs

BackgroundCytokine-induced killer cells (CIKs) adoptive cell transfer (ACT) is a common malignant tumor treatment method. Interleukin-2 (IL-2) is one of essential cytokines for CIKs culture. In most studies, only the effect of IL-2 concentration on function of CIKs was studied, but the difference between multifarious adding manner of IL-2 was not explored. MethodsThis study established a novel sequential adding manner of IL-2. Different concentration of IL-2 was added in different CIKs induction phase. Then, proliferation ability of CIKs was evaluated using cell proliferation curves, immune phenotype was analyzed by flow cytometry (FCM), IFN-γ secretion ability and cytotoxicity were detected by ELISA Kit and CCK-8 Kit respectively . Multiple comparison tests were conducted between each group to compare function of CIKs in 12 experimental groups. ResultsAs the IL-2 concentration increased, the number of CIKs continued to increase in each group, but its function was not positively related with its number: CD3+ CD56+ subpopulation ratio, INF-γ secretion ability and cytotoxicity presented irregular changes. During quiescent phase and logarithmic growth phase, adding 300 and 1000 U/mL IL-2 respectively could obtain amounts of powerful CIKs (CD3+ CD56+ subpopulation ratio: 40.9%, INF-γ secretion ability: 542pg/mL, cytotoxicity: 40:1, 74.22) . ConclusionsDifferent concentration of IL-2 had a greater influence on biological function of CIKs in different growth phase, it was better to add IL-2 sequentially in quiescent phase and exponential growth phase of CIKs.

From high friction zone to frontal collapse: dynamics of an ongoing tidewater glacier surge, Negribreen, Svalbard

Negribreen, a tidewater glacier located in central eastern Svalbard, began actively surging after it experienced an initial collapse in summer 2016. The surge resulted in horizontal surface velocities of more than 25 m d−1, making it one of the fastest-flowing glaciers in the archipelago. The last surge of Negribreen likely occurred in the 1930s, but due to a long quiescent phase, investigations of this glacier have been limited. As Negribreen is part of the Negribreen Glacier System, one of the largest glacier systems in Svalbard, investigating its current surge event provides important information on surge behaviour among tidewater glaciers within the region. Here, we demonstrate the surge development and discuss triggering mechanisms using time series of digital elevation models (1969–2018), surface velocities (1995–2018), crevasse patterns and glacier extents from various data sources. We find that the active surge results from a four-stage process. Stage 1 (quiescent phase) involves a long-term, gradual geometry change due to high subglacial friction towards the terminus. These changes allow the onset of Stage 2, an accelerating frontal destabilization, which ultimately results in the collapse (Stage 3) and active surge (Stage 4).

The path to Z And-type outbursts: The case of V426 Sagittae (HBHA 1704-05)

Context. The star V426 Sge (HBHA 1704-05), originally classified as an emission-line object and a semi-regular variable, brightened at the beginning of August 2018, showing signatures of a symbiotic star outburst. Aims. We aim to confirm the nature of V426 Sge as a classical symbiotic star, determine the photometric ephemeris of the light minima, and suggest the path from its 1968 symbiotic nova outburst to the following 2018 Z And-type outburst. Methods. We re-constructed an historical light curve (LC) of V426 Sge from approximately the year 1900, and used original low- (R ∼ 500–1500; 330–880 nm) and high-resolution (R ∼ 11 000–34 000; 360–760 nm) spectroscopy complemented with Swift-XRT and UVOT, optical UBVRCIC and near-infrared JHKL photometry obtained during the 2018 outburst and the following quiescence. Results. The historical LC reveals no symbiotic-like activity from ∼1900 to 1967. In 1968, V426 Sge experienced a symbiotic nova outburst that ceased around 1990. From approximately 1972, a wave-like orbitally related variation with a period of 493.4 ± 0.7 days developed in the LC. This was interrupted by a Z And-type outburst from the beginning of August 2018 to the middle of February 2019. At the maximum of the 2018 outburst, the burning white dwarf (WD) increased its temperature to ≳2 × 105 K, generated a luminosity of ∼7 × 1037 (d/3.3 kpc)2 erg s−1 and blew a wind at the rate of ∼3 × 10−6 M⊙ yr−1. Our spectral energy distribution models from the current quiescent phase reveal that the donor is a normal M4-5 III giant characterised with Teff ∼ 3400 K, RG ∼ 106 (d/3.3 kpc) R⊙ and LG ∼ 1350 (d/3.3 kpc)2 L⊙ and the accretor is a low-mass ∼0.5 M⊙ WD. Conclusions. During the transition from the symbiotic nova outburst to the quiescent phase, a pronounced sinusoidal variation along the orbit develops in the LC of most symbiotic novae. The following eventual outburst is of Z And-type, when the accretion by the WD temporarily exceeds the upper limit of the stable burning. At this point the system becomes a classical symbiotic star.

XMM-Newton observations of the symbiotic recurrent nova T CrB: evolution of X-ray emission during the active phase

ABSTRACT We present an analysis of the XMM-Newton observations of the symbiotic recurrent nova T CrB, obtained during its active phase which started in 2014–2015. The XMM-Newton spectra of T CrB have two prominent components: a soft one (0.2–0.6 keV), well represented by blackbody emission, and a heavily absorbed hard component (2–10 keV), well matched by optically-thin plasma emission with high temperature (kT ≈ 8 keV). The XMM-Newton observations reveal evolution of the X-ray emission from T CrB in its active phase. Namely, the soft component in its spectrum is decreasing with time, while the opposite is true for the hard component. Comparison with data obtained in the quiescent phase shows that the soft component is typical only for the active phase, while the hard component is present in both phases but it is considerably stronger in the quiescent phase. Presence of stochastic variability (flickering) on time-scales of minutes and hours is confirmed both in X-rays and UV (UVM2 filter of the XMM-Newton optical monitor). On the other hand, periodic variability of 6000–6500 s is found for the first time in the soft X-ray emission (0.2–0.6 keV) from T CrB. We associate this periodic variability with the rotational period of the white dwarf in this symbiotic binary.

Detection of new eruptions in the Magellanic Clouds luminous blue variables R 40 and R 110

We performed a spectroscopic and photometric analysis to study new eruptions in two luminous blue variables (LBVs) in the Magellanic Clouds. We detected a strong new eruption in the LBV R40 that reached V ~ 9.2 in 2016, which is around 1.3 mag brighter than the minimum registered in 1985. During this new eruption, the star changed from an A-type to a late F-type spectrum. Based on photometric and spectroscopic empirical calibrations and synthetic spectral modeling, we determine that R 40 reached Teff = 5800–6300 K during this new eruption. This object is thereby probably one of the coolest identified LBVs. We could also identify an enrichment of nitrogen and r- and s-process elements. We detected a weak eruption in the LBV R 110 with a maximum of V ~ 9.9 mag in 2011, that is, around 1.0 mag brighter than in the quiescent phase. On the other hand, this new eruption is about 0.2 mag fainter than the first eruption detected in 1990, but the temperature did not decrease below 8500 K. Spitzer spectra show indications of cool dust in the circumstellar environment of both stars, but no hot or warm dust was present, except by the probable presence of PAHs in R 110. We also discuss a possible post-red supergiant nature for both stars.