Journals
2018 EN
D. K. Sahu · G. C. Anupama · N. K. Chakradhari
+4 more
We present optical and ultraviolet photometry, and low resolution opticalspectroscopy of the broad-line type Ic supernova SN 2014ad in the galaxy PGC37625 (Mrk 1309), covering the evolution of the supernova during $-$5 to +87 dwith respect to the date of maximum in $B$-band. A late phase spectrum obtainedat +340 d is also presented. With an absolute $V$ band magnitude at peak of$M_{V}$ = $-$18.86 $\pm$ 0.23 mag, SN 2014ad is fainter than Gamma Ray Burst(GRB) associated supernovae, and brighter than most of the normal andbroad-line type Ic supernovae without an associated GRB. The spectral evolutionindicates the expansion velocity of the ejecta, as measured using the Si\,{\scii} line, to be as high as $\sim$ 33500 km\,s$^{-1}$ around maximum, whileduring the post-maximum phase it settles down at $\sim$ 15000 km\,s$^{-1}$. Theexpansion velocity of SN 2014ad is higher than all other well observedbroad-line type Ic supernovae except the GRB associated SN 2010bh. Theexplosion parameters, determined by applying the Arnett's analytical lightcurve model to the observed bolometric light curve, indicate that it was anenergetic explosion with a kinetic energy of $\sim$ (1 $\pm$0.3)$\times$10$^{52}$ ergs, a total ejected mass of $\sim$ (3.3 $\pm$ 0.8)M$_\odot$, and $\sim$ 0.24 M$_\odot$ of $^{56}$Ni was synthesized in theexplosion. The metallicity of the host galaxy near the supernova region isestimated to be $\sim$ 0.5 Z$_\odot$.
Journals
2018 EN
Raya Dastidar · Kuntal Misra · G. Hosseinzadeh
+20 more
We present optical photometry and spectroscopy from about a week afterexplosion to $\sim$272 d of an atypical Type IIP supernova, SN 2015ba, whichexploded in the edge-on galaxy IC 1029. SN 2015ba is a luminous event with anabsolute V-band magnitude of -17.1$\pm$0.2 mag at 50 d since explosion and hasa long plateau lasting for $\sim$123 d. The distance to the SN is estimated tobe 34.8$\pm$0.7 Mpc using the expanding photosphere and standard candlemethods. High-velocity H-Balmer components constant with time are observed inthe late-plateau phase spectra of SN 2015ba, which suggests a possible role ofcircumstellar interaction at these phases. Both hydrodynamical and analyticalmodelling suggest a massive progenitor of SN 2015ba with a pre-explosion massof 24-26 M$_\odot$. However, the nebular spectra of SN 2015ba exhibitinsignificant levels of oxygen, which is otherwise expected from a massiveprogenitor. This might be suggestive of the non-monotonical link between O-coremasses and the zero-age main-sequence mass of pre-supernova stars and/oruncertainties in the mixing scenario in the ejecta of supernovae.
Journals
2018 EN
A. Zurlo · R. Gratton · D. Mesa
+19 more
Proxima Centauri, our closest stellar neighbour, is a low-mass M5 dwarforbiting in a triple system. An Earth-mass planet with an 11 day period hasbeen discovered around this star. The star's mass has been estimated onlyindirectly using a mass-luminosity relation, meaning that large uncertaintiesaffect our knowledge of its properties. To refine the mass estimate, anindependent method has been proposed: gravitational microlensing. By takingadvantage of the close passage of Proxima Cen in front of two background stars,it is possible to measure the astrometric shift caused by the microlensingeffect due to these close encounters and estimate the gravitational mass of thelens (Proxima Cen). Microlensing events occurred in 2014 and 2016 with impactparameters, the closest approach of Proxima Cen to the background star, of1\farcs6 $\pm$ 0\farcs1 and 0\farcs5 $\pm$ 0\farcs1, respectively. Accuratemeasurements of the positions of the background stars during the last two yearshave been obtained with HST/WFC3, and with VLT/SPHERE from the ground. TheSPHERE campaign started on March 2015, and continued for more than two years,covering 9 epochs. The parameters of Proxima Centauri's motion on the sky,along with the pixel scale, true North, and centering of the instrumentdetector were readjusted for each epoch using the background stars visible inthe IRDIS field of view. The experiment has been successful and the astrometricshift caused by the microlensing effect has been measured for the second eventin 2016. We used this measurement to derive a mass of0.150$^{\textrm{+}0.062}_{-0.051}$ (an error of $\sim$ 40\%) \MSun for ProximaCentauri acting as a lens. This is the first and the only currently possiblemeasurement of the gravitational mass of Proxima Centauri.
Journals
2018 EN
Dipen Sahu · Young-Chol Minh · Chin-Fei Lee
+4 more
HH212, a nearby (400 pc) object in Orion, is a Class 0 protostellar systemwith a Keplerian disk and collimated bipolar SiO jets. Deuterated water, HDOand a deuterated complex molecule, methanol (CH2DOH) have been reported in thesource. Here, we report the HDCO (deuterated formaldehyde) line observationfrom ALMA data to probe the inner region of HH212. We compare HDCO line withother molecular lines to understand the possible chemistry and physics of thesource. The distribution of HDCO emission suggests it may be associated withthe base of the outflow. The emission also shows a rotation but it is notassociated with the Keplerian rotation of disk or the rotating infallingenvelope, rather it is associated with the outflow as previously seen in C 34S. From the possible deuterium fractionation, we speculate that the gas phaseformation of deuterated formaldehyde is active in the central hot region of thelow-mass protostar system, HH212.
Journals
2018 EN
Avinash Singh · S. Srivastav · Brajesh Kumar
+2 more
Optical broadband (UBVRI) photometric and low-resolution spectroscopicobservations of the type II-P supernova (SN) ASASSN-14dq are presented.ASASSN-14dq exploded in a low-luminosity/metallicity host galaxy UGC 11860, thesignatures of which are present as weak iron lines in the photospheric phasespectra. The SN has a plateau duration of $\sim\,$90 d, with a plateau declinerate of 1.38 $\rm mag\ (100 d)^{-1}$ in V-band which is higher than most typeII-P SNe. ASASSN-14dq is a luminous type II-P SN with a peak $V$-band absolutemagnitude of -17.7$\,\pm\,$0.2 mag. The light curve of ASASSN-14dq indicates itto be a fast-declining type II-P SN, making it a transitional event between thetype II-P and II-L SNe. The empirical relation between the steepness parameterand $\rm ^{56}Ni$ mass for type II SNe was rebuilt with the help ofwell-sampled light curves from the literature. A $\rm ^{56}Ni$ mass of$\sim\,$0.029 M$_{\odot}$ was estimated for ASASSN-14dq, which is slightlylower than the expected $\rm ^{56}Ni$ mass for a luminous type II-P SN. Usinganalytical light curve modelling, a progenitor radius of $\rm\sim3.6\times10^{13}$ cm, an ejecta mass of $\rm \sim10\ M_{\odot}$ and a totalenergy of $\rm \sim\,1.8\times 10^{51}$ ergs was estimated for this event. Thephotospheric velocity evolution of ASASSN-14dq resembles a type II-P SN, butthe Balmer features (H$\alpha$ and H$\beta$) show relatively slow velocityevolution. The high-velocity H$\alpha$ feature in the plateau phase, theasymmetric H$\alpha$ emission line profile in the nebular phase and theinferred outburst parameters indicate an interaction of the SN ejecta with thecircumstellar material (CSM).
Journals
2018 EN
Snehalata Sahu · Annapurni Subramaniam · Patrick Côté
+2 more
A complete census of Blue Horizontal Branch (BHB) and Blue Straggler Star(BSS) population within the 10$'$ radius from the center of the GlobularCluster, NGC 288 is presented, based on the images from the Ultraviolet ImagingTelescope (UVIT). The UV and UV$-$optical Colour-Magnitude Diagrams (CMDs) areconstructed by combining the UVIT, HST-ACS and ground data and compared withthe BaSTI isochrones generated for UVIT filters. We used stellar proper motionsdata from GAIA DR2 to select the cluster members. Our estimations of thetemperature distribution of 110 BHB stars reveal two peaks with the main peakat $T_{eff}\sim$ 10,300 K with the distribution extending up to $T_{eff}\sim$18,000 K. We identify the well known photometric gaps including the G-jump inthe BHB distribution which are located between the peaks. We detect a plateauin the FUV magnitude for stars hotter than $T_{eff}\sim$ 11,500 K (G-jump),which could be due to the effect of atomic diffusion. We detect 2 Extreme HB(EHB) candidates with temperatures ranging from 29,000 to 32,000 K. The radialdistribution of 68 BSSs suggests that the bright BSSs are more centrallyconcentrated than the faint BSS and the BHB distribution. We find that the BSSshave a mass range of 0.86 - 1.25 M$_{\odot}$ and an age range of 2 - 10 Gyrwith a peak at 1 M$_{\odot}$ and 4 Gyr respectively. This study showcases theimportance of combining UVIT with HST, ground, and GAIA data in deriving HB andBSS properties.
Journals
2018 EN
N. Kains · A. Calamida · M. Rejkuba
+8 more
We report the detection of 1143 variable stars towards the Galactic bulge,including 320 previously uncatalogued variables, using time-series photometryextracted from data obtained with the VIMOS imager at the Very Large Telescope.Observations of the Sagittarius Window Eclipsing Extrasolar Planet Search(SWEEPS) field in the Galactic Bulge were taken over 2 years between March andOctober at a cadence of $\sim$ 4 days, enabling the detection of variables withperiods up to $\sim$100 days. Many of these were already known, but we detecteda significant number of new variables, including 26 Cepheids, a further 18Cepheid candidates, and many contact binaries. Here we publish the catalog ofthe new variables, containing coordinates, mean magnitudes as well as periodsand classification; full light curves for these variables are also madeavailable electronically.
Journals
2018 EN
Anjasha Gangopadhyay · Kuntal Misra · A. Pastorello
+14 more
We present results of the photometric (from 3 to 509 days past explosion) andspectroscopic (up to 230 days past explosion) monitoring campaign of theHe-rich Type IIb supernova (SN) 2015as. The {\it (B-V)} colour evolution of SN2015as closely resemble those of SN 2008ax, suggesting that SN 2015as belongsto the SN IIb subgroup that does not show the early, short-duration photometricpeak. The light curve of SN 2015as reaches the $B$-band maximum about 22 daysafter the explosion, at an absolute magnitude of -16.82 $\pm$ 0.18 mag. At$\sim$ 75 days after the explosion, its spectrum transitions from that of a SNII to a SN Ib. P~Cygni features due to He I lines appear at around 30 daysafter explosion, indicating that the progenitor of SN 2015as was partiallystripped. For SN~2015as, we estimate a $^{56}$Ni mass of $\sim$ 0.08M$_{\odot}$ and ejecta mass of 1.1--2.2 M$_{\odot}$, which are similar to thevalues inferred for SN 2008ax. The quasi bolometric analytical light curvemodelling suggests that the progenitor of SN 2015as has a modest mass ($\sim$0.1 M$_{\odot}$), a nearly-compact ($\sim$ 0.05$\times$10$^{13}$ cm) H envelopeon top of a dense, compact ($\sim$ 2$\times$10$^{11}$ cm) and a more massive($\sim$ 1.2 M$_{\odot}$) He core. The analysis of the nebular phase spectraindicates that $\sim$ 0.44 M$_{\odot}$ of O is ejected in the explosion. Theintensity ratio of the [Ca II]/[O I] nebular lines favours either a mainsequence progenitor mass of $\sim$ 15 M$_{\odot}$ or a Wolf Rayet star of 20M$_{\odot}$.
Journals
2018 EN
Christine Feld · Peeyush Sahu · Miriam Frech
+5 more
SKI is a transcriptional co-regulator and overexpressed in various human tumors, for example in acute myeloid leukemia (AML). SKI contributes to the origin and maintenance of the leukemic phenotype. Here, we use ChIP-seq and RNA-seq analysis to identify the epigenetic alterations induced by SKI overexpression in AML cells. We show that approximately two thirds of differentially expressed genes are up-regulated upon SKI deletion, of which >40% harbor SKI binding sites in their proximity, primarily in enhancer regions. Gene ontology analysis reveals that many of the differentially expressed genes are annotated to hematopoietic cell differentiation and inflammatory response, corroborating our finding that SKI contributes to a myeloid differentiation block in HL60 cells. We find that SKI peaks are enriched for RUNX1 consensus motifs, particularly in up-regulated SKI targets upon SKI deletion. RUNX1 ChIP-seq displays that nearly 70% of RUNX1 binding sites overlap with SKI peaks, mainly at enhancer regions. SKI and RUNX1 occupy the same genomic sites and cooperate in gene silencing. Our work demonstrates for the first time the predominant co-repressive function of SKI in AML cells on a genome-wide scale and uncovers the transcription factor RUNX1 as an important mediator of SKI-dependent transcriptional repression.
Journals
2018 EN
Boehr David D. · O'Rourke Kathleen F. · D'Amico Rebecca N.
+1 more
Networks of noncovalent interactions play important roles in the structural dynamics of globular proteins. Allosteric signals can propagate from the surface of an enzyme into its active site through these amino acid interaction networks. We used nuclear magnetic resonance (NMR) chemical shift covariance analyses 1 on a catalytically inactive variant of the alpha subunit of tryptophan synthase to map amino acid interaction networks across its entire catalytic cycle. We used site‐specific Ala‐to‐Gly substitutions at loop residues to generate small network perturbations 2 . The amino acid substitutions lead to chemical shift changes both local and remote from the site(s) of perturbations. Residues with covarying chemical shift changes across this series of perturbations are proposed to be involved in the same conformational change, and thus belong to the same amino acid interaction network 3 . Our studies indicate that different enzyme states have different sets of chemical shift correlations, the chemical shift correlations change as a function of the catalytic cycle, and the changes in chemical shift correlations are coordinated with each other. These studies indicate that long‐range interaction networks systematically strengthen (or weaken) as a function of catalytic cycle progression. Most residues identified in these networks are dynamic on the μs‐ms timescale according to NMR 15 N R 2 relaxation dispersion studies 4 . Amino acid substitutions at surface‐exposed, network positions lead to the suppression of these structural dynamics and abrogate the stimulation of the alpha subunit's catalytic activity by the beta subunit. The evolving long‐range interaction networks are likely important in positioning catalytic machinery, controlling protein structural dynamics, and coordinating functional interactions with the beta subunit. In general, amino acid interaction networks offer opportunities to modify state‐specific enzyme function and regulation. Support or Funding Information NSF MCB‐1615032 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
The Federation of American Societies for Experimental Biology