161 research outputs found
Modeling the Multiwavelength Evolution of the V960 Mon System
We study the evolution of the FU Ori object V960 Mon since its outburst,
using available multi-wavelength photometric time series over 8 years,
complemented by several epochs of moderate-dispersion spectrophotometry. We
find that the source fading can be well-described by a decrease in the
temperature of the inner disk, which results from a combination of decreasing
accretion rate and increasing inner disk radius. We model the system with a
disk atmosphere model that produces the observed variations in multi-band
photometry (this paper) and high resolution spectral lines (a companion paper).Comment: 15 pages, 13 figures, 2 tables, Accepted to Ap
Resolving Decades of Periodic Spirals from the Wolf-Rayet Dust Factory WR 112
WR 112 is a dust-forming carbon-rich Wolf-Rayet (WC) binary with a dusty
circumstellar nebula that exhibits a complex asymmetric morphology, which
traces the orbital motion and dust formation in the colliding winds of the
central binary. Unraveling the complicated circumstellar dust emission around
WR 112 therefore provides an opportunity to understand the dust formation
process in colliding-wind WC binaries. In this work, we present a multi-epoch
analysis of the circumstellar dust around WR 112 using seven high spatial
resolution (FWHM ) N-band ( m) imaging
observations spanning almost 20 years and includes newly obtained images from
Subaru/COMICS in Oct 2019. In contrast to previous interpretations of a face-on
spiral morphology, we observe clear evidence of proper motion of the
circumstellar dust around WR 112 consistent with a nearly edge-on spiral with a
half-opening angle and a -yr period. The revised
near edge-on geometry of WR 112 reconciles previous observations of highly
variable non-thermal radio emission that was inconsistent with a face-on
geometry. We estimate a revised distance to WR 112 of kpc based on the observed dust expansion rate and a
spectroscopically derived WC terminal wind velocity of
km s. With the newly derived WR 112 parameters we fit optically-thin
dust spectral energy distribution models and determine a dust production rate
of M yr, which
demonstrates that WR 112 is one of the most prolific dust-making WC systems
known.Comment: 17 pages, 9 figures, 1 animated gif, accepted for publication in Ap
Resolving Decades of Periodic Spirals from the Wolf–Rayet Dust Factory WR 112
WR 112 is a dust-forming carbon-rich Wolf–Rayet (WC) binary with a dusty circumstellar nebula that exhibits a complex asymmetric morphology, which traces the orbital motion and dust formation in the colliding winds of the central binary. Unraveling the complicated circumstellar dust emission around WR 112 therefore provides an opportunity to understand the dust formation process in colliding-wind WC binaries. In this work, we present a multi-epoch analysis of the circumstellar dust around WR 112 using seven high spatial resolution (FWHM ~ 0farcs3–0farcs4) N-band (λ ~ 12 μm) imaging observations spanning almost 20 yr and that includes images obtained from Subaru/COMICS in 2019 October. In contrast to previous interpretations of a face-on spiral morphology, we observe clear evidence of proper motion of the circumstellar dust around WR 112 consistent with a nearly edge-on spiral with a θ_s = 55° half-opening angle and a ~20 yr period. The revised near edge-on geometry of WR 112 reconciles previous observations of highly variable nonthermal radio emission that was inconsistent with a face-on geometry. We estimate a revised distance to WR 112 of d = 3.39_(-0.84)^(+0.89) kpc based on the observed dust expansion rate and a spectroscopically derived WC terminal wind velocity of v_∞ = 1230 ± 260 km s⁻¹. With the newly derived WR 112 parameters, we fit optically thin dust spectral energy distribution models and determine a dust production rate of Ṁ_d = 2.7_(-1.3)^(+1.0) x 10⁻⁶ M_⊙ yr⁻¹, which demonstrates that WR 112 is one of the most prolific dust-making WC systems known
Vertebrate ancient opsin photopigment spectra and the avian photoperiodic response
In mammals, photoreception is restricted to cones, rods and a subset of retinal ganglion cells. By contrast, non-mammalian vertebrates possess many extraocular photoreceptors but in many cases the role of these photoreceptors and their underlying photopigments is unknown. In birds, deep brain photoreceptors have been shown to sense photic changes in daylength (photoperiod) and mediate seasonal reproduction. Nonetheless, the specific identity of the opsin photopigment ‘sensor’ involved has remained elusive. Previously, we showed that vertebrate ancient (VA) opsin is expressed in avian hypothalamic neurons and forms a photosensitive molecule. However, a direct functional link between VA opsin and the regulation of seasonal biology was absent. Here, we report the in vivo and in vitro absorption spectra (λmax = ∼490 nm) for chicken VA photopigments. Furthermore, the spectral sensitivity of these photopigments match the peak absorbance of the avian photoperiodic response (λmax = 492 nm) and permits maximum photon capture within the restricted light environment of the hypothalamus. Such a correspondence argues strongly that VA opsin plays a key role in regulating seasonal reproduction in birds
Discovery of an intermediate-luminosity red transient in M51 and its likely dust-obscured, infrared-variable progenitor
We present the discovery of an optical transient (OT) in Messier 51,
designated M51 OT2019-1 (also ZTF19aadyppr, AT 2019abn, ATLAS19bzl), by the
Zwicky Transient Facility (ZTF). The OT rose over 15 days to an observed
luminosity of (), in the
luminosity gap between novae and typical supernovae (SNe). Spectra during the
outburst show a red continuum, Balmer emission with a velocity width of
km s, Ca II and [Ca II] emission, and absorption features
characteristic of an F-type supergiant. The spectra and multiband light curves
are similar to the so-called "SN impostors" and intermediate-luminosity red
transients (ILRTs). We directly identify the likely progenitor in archival
Spitzer Space Telescope imaging with a m luminosity of
and a color redder than 0.74 mag, similar
to those of the prototype ILRTs SN 2008S and NGC 300 OT2008-1. Intensive
monitoring of M51 with Spitzer further reveals evidence for variability of the
progenitor candidate at [4.5] in the years before the OT. The progenitor is not
detected in pre-outburst Hubble Space Telescope optical and near-IR images. The
optical colors during outburst combined with spectroscopic temperature
constraints imply a higher reddening of mag and higher
intrinsic luminosity of
() near peak than seen in previous ILRT
candidates. Moreover, the extinction estimate is higher on the rise than on the
plateau, suggestive of an extended phase of circumstellar dust destruction.
These results, enabled by the early discovery of M51 OT2019-1 and extensive
pre-outburst archival coverage, offer new clues about the debated origins of
ILRTs and may challenge the hypothesis that they arise from the
electron-capture induced collapse of extreme asymptotic giant branch stars.Comment: 21 pages, 5 figures, published in ApJ
Constraining the X-ray - Infrared spectral index of second-timescale flares from SGR1935+2154 with Palomar Gattini-IR
The Galactic magnetar SGR1935+2154 has been reported to produce the first
known example of a bright millisecond duration radio burst (FRB 200428) similar
to the cosmological population of fast radio bursts (FRBs), bolstering the
association of FRBs to active magnetars. The detection of a coincident bright
X-ray burst has revealed the first observed multi-wavelength counterpart of a
FRB. However, the search for similar emission at optical wavelengths has been
hampered by the high inferred extinction on the line of sight. Here, we present
results from the first search for second-timescale emission from the source at
near-infrared wavelengths using the Palomar Gattini-IR observing system in
J-band, made possible by a recently implemented detector read-out mode that
allowed for short exposure times of 0.84 s with 99.9% observing efficiency.
With a total observing time of 12 hours (47728 images) on source, we place
median limits on the second-timescale emission of mJy (13.1
AB mag). We present non-detection limits from epochs of four simultaneous X-ray
bursts detected by the Insight-{\it HXMT} and {\it NuSTAR} telescopes during
our observing campaign. The limits translate to an extinction corrected fluence
limit of Jy ms for an estimated extinction of mag. These
limits provide the most stringent constraints to date on the fluence of flares
at frequencies of Hz, and constrain the ratio of the
near-infrared (NIR) fluence to that of coincident X-ray bursts to . Our observations were sensitive enough to easily detect
a near-infrared counterpart of FRB 200428 if the NIR emission falls on the same
power law as that observed across its radio to X-ray spectrum. The
non-detection of NIR emission around the coincident X-ray bursts constrains the
fluence index of the brightest burst to be steeper than .Comment: 10 pages, 4 figures, submitted to ApJL. Comments welcom
Differential Expression of Melanopsin Isoforms Opn4L and Opn4S during Postnatal Development of the Mouse Retina
Photosensitive retinal ganglion cells (pRGCs) respond to light from birth and represent the earliest known light detection system to develop in the mouse retina. A number of morphologically and functionally distinct subtypes of pRGCs have been described in the adult retina, and have been linked to different physiological roles. We have previously identified two distinct isoforms of mouse melanopsin, Opn4L and Opn4S, which are generated by alternate splicing of the Opn4 locus. These isoforms are differentially expressed in pRGC subtypes of the adult mouse retina, with both Opn4L and Opn4S detected in M1 type pRGCs, and only Opn4L detected in M2 type pRGCs. Here we investigate the developmental expression of Opn4L and Opn4S and show a differential profile of expression during postnatal development. Opn4S mRNA is detected at relatively constant levels throughout postnatal development, with levels of Opn4S protein showing a marked increase between P0 and P3, and then increasing progressively over time until adult levels are reached by P10. By contrast, levels of Opn4L mRNA and protein are low at birth and show a marked increase at P14 and P30 compared to earlier time points. We suggest that these differing profiles of expression are associated with the functional maturation of M1 and M2 subtypes of pRGCs. Based upon our data, Opn4S expressing M1 type pRGCs mature first and are the dominant pRGC subtype in the neonate retina, whereas increased expression of Opn4L and the maturation of M2 type pRGCs occurs later, between P10 and P14, at a similar time to the maturation of rod and cone photoreceptors. We suggest that the distinct functions associated with these cell types will develop at different times during postnatal development
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