We present a data set of images of the gravitationally lensed quasar Q2237+0305, that was obtained at the Apache Point Observatory (APO) between June 1995 and January 1998. Although the images were ...taken under variable, often poor seeing conditions and with coarse pixel sampling, photometry is possible for the two brighter quasar images A and B with the help of exact quasar image positions from HST observations. We obtain a light curve with 73 data points for each of the images A and B. There is evidence for a long ($\ga$100 day) brightness peak in image A in 1996 with an amplitude of about 0.4 to 0.5 mag (relative to 1995), which indicates that microlensing has been taking place in the lensing galaxy. Image B does not vary much over the course of the observation period. The long, smooth variation of the light curve is similar to the results from the OGLE monitoring of the system (Woźniak et al. CITE).
Understanding the late-stage evolution of the most massive stars such as
$\eta$ Carinae is challenging because no true analogs of $\eta$ Car have been
clearly identified in the Milky Way or other ...galaxies. In Khan et. al. (2013),
we utilized Spitzer IRAC images of $7$ nearby ($\lesssim4$ Mpc) galaxies to
search for such analogs, and found $34$ candidates with flat or red mid-IR
spectral energy distributions. Here, in Paper II, we present our
characterization of these candidates using multi-wavelength data from the
optical through the far-IR. Our search detected no true analogs of $\eta$ Car,
which implies an eruption rate that is a fraction $0.01\lesssim F \lesssim
0.19$ of the ccSN rate. This is roughly consistent with each $M_{ZAMS} \gtrsim
70M_\odot$ star undergoing $1$ or $2$ outbursts in its lifetime. However, we do
identify a significant population of $18$ lower luminosity
$\left(\log(L/L_\odot)\simeq5.5-6.0\right)$ dusty stars. Stars enter this phase
at a rate that is fraction $0.09 \lesssim F \lesssim 0.55$ of the ccSN rate,
and this is consistent with all $25 < M_{ZAMS} < 60M_\odot$ stars undergoing an
obscured phase at most lasting a few thousand years once or twice. These phases
constitute a negligible fraction of post-main sequence lifetimes of massive
stars, which implies that these events are likely to be associated with special
periods in the evolution of the stars. The mass of the obscuring material is of
order $\sim M_\odot$, and we simply do not find enough heavily obscured stars
for theses phases to represent more than a modest fraction ($\sim 10\%$ not
$\sim 50\%$) of the total mass lost by these stars. In the long term, the
sources that we identified will be prime candidates for detailed physical
analysis with JWST.
We present the discovery of KELT-1b, the first transiting low-mass companion from the wide-field Kilodegree Extremely Little Telescope-North (KELT-North) survey. The V=10.7 primary is a mildly ...evolved, solar-metallicity, mid-F star. The companion is a low-mass brown dwarf or super-massive planet with mass of 27.23+/-0.50 MJ and radius of 1.110+0.037-0.024 RJ, on a very short period (P=1.21750007) circular orbit. KELT-1b receives a large amount of stellar insolation, with an equilibrium temperature assuming zero albedo and perfect redistribution of 2422 K. Upper limits on the secondary eclipse depth indicate that either the companion must have a non-zero albedo, or it must experience some energy redistribution. Comparison with standard evolutionary models for brown dwarfs suggests that the radius of KELT-1b is significantly inflated. Adaptive optics imaging reveals a candidate stellar companion to KELT-1, which is consistent with an M dwarf if bound. The projected spin-orbit alignment angle is consistent with zero stellar obliquity, and the vsini of the primary is consistent with tidal synchronization. Given the extreme parameters of the KELT-1 system, we expect it to provide an important testbed for theories of the emplacement and evolution of short-period companions, and theories of tidal dissipation and irradiated brown dwarf atmospheres.
We present very early UV to optical photometric and spectroscopic observations of the peculiar Type IIn supernova (SN) 2011ht in UGC 5460. The UV observations of the rise to peak are only the second ...ever recorded for a Type IIn SN and are by far the most complete. The SN, first classified as a SN impostor, slowly rose to a peak of M_V \sim -17 in \sim55 days. In contrast to the \sim2 magnitude increase in the v-band light curve from the first observation until peak, the UV flux increased by >7 magnitudes. The optical spectra are dominated by strong, Balmer emission with narrow peaks (FWHM\sim600 km/s), very broad asymmetric wings (FWHM\sim4200 km/s), and blue shifted absorption (\sim300 km/s) superposed on a strong blue continuum. The UV spectra are dominated by FeII, MgII, SiII, and SiIII absorption lines broadened by \sim1500 km/s. Merged X-ray observations reveal a L_(0.2-10)=(1.0+/-0.2)x10^(39) erg/s. Some properties of SN 2011ht are similar to SN impostors, while others are comparable to Type IIn SNe. Early spectra showed features typical of luminous blue variables at maximum and during giant eruptions. However, the broad emission profiles coupled with the strong UV flux have not been observed in previous SN impostors. The absolute magnitude and energetics (~2.5x10^(49) ergs in the first 112 days) are reminiscent of normal Type IIn SN, but the spectra are of a dense wind. We suggest that the mechanism for creating this unusual profile could be a shock interacting with a shell of material that was ejected a year before the discovery of the SN.
We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we ...detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe. Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This indicates that the progenitor of SN 2009nr is not associated with a young stellar population, calling into question the conventional association of luminous SNe Ia with the "prompt" component directly correlated with current star formation. The pre-discovery observation of SN 2009nr using ASAS demonstrates the science utility of high cadence all sky surveys conducted using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.
In vivo Kinetics of Cajal Body Components Dundr, Miroslav; Hebert, Michael D.; Karpova, Tatiana S. ...
The Journal of cell biology,
03/2004, Letnik:
164, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Cajal bodies (CBs) are subnuclear domains implicated in small nuclear ribonucleoprotein (snRNP) biogenesis. In most cell types, CBs coincide with nuclear gems, which contain the survival of motor ...neurons (SMN) complex, an essential snRNP assembly factor. Here, we analyze the exchange kinetics of multiple components of CBs and gems in living cells using photobleaching microscopy. We demonstrate differences in dissociation kinetics of CB constituents and relate them to their functions. Coilin and SMN complex members exhibit relatively long CB residence times, whereas components of snRNPs, small nucleolar RNPs, and factors shared with the nucleolus have significantly shorter residence times. Comparison of the dissociation kinetics of these shared proteins from either the nucleolus or the CB suggests the existence of compartment-specific retention mechanisms. The dynamic properties of several CB components do not depend on their interaction with coilin because their dissociation kinetics are unaltered in residual nuclear bodies of coilin knockout cells. Photobleaching and fluorescence resonance energy transfer experiments demonstrate that coilin and SMN can interact within CBs, but their interaction is not the major determinant of their residence times. These results suggest that CBs and gems are kinetically independent structures.
We present a detailed study of the 2017 eruption of the classical nova
ASASSN-17pf (LMCN 2017-11a), which is located in the Large Magellanic Cloud,
including data from AAVSO, ASAS-SN, SALT, SMARTS, ...SOAR, and the Neil Gehrels
\textit{Swift} Observatory. The optical light-curve is characterized by
multiple maxima (flares) on top of a slowly evolving light-curve (with a
decline time, $t_2>$ 100 d). The maxima correlate with the appearance of new
absorption line systems in the optical spectra characterized by increasing
radial velocities. We suggest that this is evidence of multiple episodes of
mass-ejection with increasing expansion velocities. The line profiles in the
optical spectra indicate very low expansion velocities (FWHM $\sim$ 190 km
s$^{-1}$), making this nova one of the slowest expanding ever observed,
consistent with the slowly evolving light-curve. The evolution of the colors
and spectral energy distribution show evidence of decreasing temperatures and
increasing effective radii for the pseudo-photosphere during each maximum. The
optical and infrared light-curves are consistent with dust formation 125 days
post-discovery. We speculate that novae showing several optical maxima have
multiple mass-ejection episodes leading to shocks that may drive $\gamma$-ray
emission and dust formation.
We present the results from a detailed analysis of photometric and spectrophotometric data on five Seyfert 1 galaxies observed as a part of a recent reverberation mapping program. The data were ...collected at several observatories over a 140-day span beginning in 2010 August and ending in 2011 January. We obtained high sampling-rate light curves for Mrk 335, Mrk 1501, 3C120, Mrk 6, and PG2130+099, from which we have measured the time lag between variations in the 5100 Angstrom continuum and the H-beta broad emission line. We then used these measurements to calculate the mass of the supermassive black hole at the center of each of these galaxies. Our new measurements substantially improve previous measurements of MBH and the size of the broad line-emitting region for four sources and add a measurement for one new object. Our new measurements are consistent with photoionization physics regulating the location of the broad line region in active galactic nuclei.
We report the discovery of a stripped giant + lower giant binary, 2M04123153+6738486 (2M0412), identified during a search for non-interacting compact object-star binaries. 2M0412 is an evolved ...(\(T_{\rm eff, giant}\simeq4000\) K), luminous (\(L_{\rm giant}\simeq150~L_\odot\)) red giant in a circular \(P=81.2\) day binary. 2M0412 is a known variable star previously classified as a semi-regular variable. The cross-correlation functions of follow-up Keck/HIRES and LBT/PEPSI spectra show an RV-variable second component with implied mass ratio \(q=M_{\rm giant}/M_{\rm comp}\simeq0.20\pm0.01\). The ASAS-SN, ATLAS, TESS and ZTF light curves show that the giant is a Roche lobe filling ellipsoidal variable with an inclination of \(49.4^\circ{}\pm{0.3^{\circ}}\), and a giant mass of \(M_{\rm giant}=0.38\pm0.01~ M_\odot\) for a distance of \(\simeq3.7\) kpc. The mass of the giant indicates that its envelope has been stripped. The giant companion on the lower red giant branch has a mass of \(M_{\rm comp}=1.91\pm0.03~M_\odot\) with \(T_{\rm eff, comp}\simeq5000\) K, \(L_{\rm comp}\simeq60~L_\odot\) and \(R_{\rm comp}\simeq11~R_\odot\). We also identify an orbital phase dependent, broad \(\rm H\alpha\) emission line which could indicate ongoing accretion from the stripped red giant onto the companion.
The late-stage evolution of very massive stars such as $\eta$ Carinae may be
dominated by episodic mass ejections which may later lead to Type II
superluminous supernova (SLSN-II; e.g., SN 2006gy). ...However, as long as $\eta$
Car is one of a kind, it is nearly impossible to quantitatively evaluate these
possibilities. Here we announce the discovery of five objects in the nearby
($\sim4-8$ Mpc) massive star-forming galaxies M51, M83, M101 and NGC6946 that
have optical through mid-IR photometric properties consistent with the hitherto
unique $\eta$ Car. The Spitzer mid-IR spectral energy distributions of these
$L_{bol}\simeq3-8\times10^{6} L_\odot$ objects rise steeply in the $3.6-8 \mu$m
bands, then turn over between $8$ and $24 \mu$m, indicating the presence of
warm ($\sim400-600$ K) circumstellar dust. Their optical counterparts in HST
images are $\sim1.5-2$ dex fainter than their mid-IR peaks and require the
presence of $\sim5-10 M_\odot$ of obscuring material. Our finding implies that
the rate of $\eta$ Car-like events is a fraction $f=0.094$ ($0.040 < f < 0.21$
at $90\%$ confidence) of the core-collapse supernova (ccSN) rate. If there is
only one eruption mechanism and SLSN-II are due to ccSN occurring inside these
dense shells, then the ejection mechanism is likely associated with the onset
of carbon burning ($\sim 10^3 - 10^4$ years) which is also consistent with the
apparent ages of massive Galactic shells.
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