41 research outputs found
Spitzer Observations of Long-term Infrared Variability among Young Stellar Objects in Chamaeleon I
Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about 1 month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster, whose low declination makes it observable by the Spitzer Space Telescope over a 200-day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find that such variability is common, occurring in ~80% of the detected cluster members. The change in [3.6]â[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200-day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ~0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic
Spitzer Observations of Long-term Infrared Variability among Young Stellar Objects in Chamaeleon I
Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited to total baselines of about 1 month due to the orientation of the spacecraft. Here we present observations of the Chameleon I cluster, whose low declination makes it observable by the Spitzer Space Telescope over a 200-day period. We observe 30 young stellar objects with a daily cadence to better sample variability on timescales of months. We find that such variability is common, occurring in ~80% of the detected cluster members. The change in [3.6]â[4.5] color over 200 days for many of the sources falls between that expected for extinction and fluctuations in disk emission. With our high cadence and long baseline we can derive power spectral density curves covering two orders of magnitude in frequency and find significant power at low frequencies, up to the boundaries of our 200-day survey. Such long timescales are difficult to explain with variations driven by the interaction between the disk and stellar magnetic field, which has a dynamical timescale of days to weeks. The most likely explanation is either structural or temperature fluctuations spread throughout the inner ~0.5 au of the disk, suggesting that the intrinsic dust structure is highly dynamic
A Cool and Inflated Progenitor Candidate for the Type Ib Supernova 2019yvr at 2.6 Years Before Explosion
We present Hubble Space Telescope imaging of a pre-explosion counterpart to
SN 2019yvr obtained 2.6 years before its explosion as a type Ib supernova (SN
Ib). Aligning to a post-explosion Gemini-S/GSAOI image, we demonstrate that
there is a single source consistent with being the SN 2019yvr progenitor
system, the second SN Ib progenitor candidate after iPTF13bvn. We also analyzed
pre-explosion Spitzer/IRAC imaging, but we do not detect any counterparts at
the SN location. SN 2019yvr was highly reddened, and comparing its spectra and
photometry to those of other, less extinguished SNe Ib we derive
mag for SN 2019yvr. Correcting photometry
of the pre-explosion source for dust reddening, we determine that this source
is consistent with a and K star. This relatively cool photospheric
temperature implies a radius of 320, much larger
than expectations for SN Ib progenitor stars with trace amounts of hydrogen but
in agreement with previously identified SN IIb progenitor systems. The
photometry of the system is also consistent with binary star models that
undergo common envelope evolution, leading to a primary star hydrogen envelope
mass that is mostly depleted but seemingly in conflict with the SN Ib
classification of SN 2019yvr. SN 2019yvr had signatures of strong circumstellar
interaction in late-time (150 day) spectra and imaging, and so we consider
eruptive mass loss and common envelope evolution scenarios that explain the SN
Ib spectroscopic class, pre-explosion counterpart, and dense circumstellar
material. We also hypothesize that the apparent inflation could be caused by a
quasi-photosphere formed in an extended, low-density envelope or circumstellar
matter around the primary star.Comment: 22 pages, 9 figures, submitted to MNRA
Seven years of coordinated ChandraâNuSTAR observations of SN 2014C unfold the extreme mass-loss history of its stellar progenitor
We present the results from our 7 yr long broadband X-ray observing campaign of SN 2014C with Chandra and NuSTAR. These coordinated observations represent the first look at the evolution of a young extragalactic SN in the 0.3â80 keV energy range in the years after core collapse. We find that the spectroscopic metamorphosis of SN 2014C from an ordinary type Ib SN into an interacting SN with copious hydrogen emission is accompanied by luminous X-rays reaching L x â 5.6 Ă 1040 erg sâ1 (0.3â100 keV) at âŒ1000 days post-explosion and declining as L x â t â1 afterwards. The broadband X-ray spectrum is of thermal origin and shows clear evidence for cooling after peak, with T(t)â20keV(t/tpk)â0.5 . Soft X-rays of sub-keV energy suffer from large photoelectric absorption originating from the local SN environment with NHint(t)â3Ă1022(t/400days)â1.4cmâ2 . We interpret these findings as the result of the interaction of the SN shock with a dense (n â 105 â 106 cmâ3), H-rich disk-like circumstellar medium (CSM) with inner radius âŒ2 Ă 1016 cm and extending to âŒ1017 cm. Based on the declining NHint(t) and X-ray luminosity evolution, we infer a CSM mass of âŒ(1.2 fâ2.0 f)Mâ , where f is the volume filling factor. We place SN 2014C in the context of 121 core-collapse SNe with evidence for strong shock interaction with a thick circumstellar medium. Finally, we highlight the challenges that the current mass-loss theories (including wave-driven mass loss, binary interaction, and line-driven winds) face when interpreting the wide dynamic ranges of CSM parameters inferred from observations
Radio analysis of SN2004C reveals an unusual CSM density profile as a harbinger of core collapse
We present extensive multifrequency Karl G. Jansky Very Large Array (VLA) and Very Long Baseline Array (VLBA) observations of the radio-bright supernova (SN) IIb SN 2004C that span âŒ40â2793 days post-explosion. We interpret the temporal evolution of the radio spectral energy distribution in the context of synchrotron self-absorbed emission from the explosion's forward shock as it expands in the circumstellar medium (CSM) previously sculpted by the mass-loss history of the stellar progenitor. VLBA observations and modeling of the VLA data point to a blastwave with average velocity âŒ0.06 c that carries an energy of â1049 erg. Our modeling further reveals a flat CSM density profile ÏCSM â Râ0.03±0.22 up to a break radius Rbr â (1.96 ± 0.10) Ă 1016 cm, with a steep density gradient following ÏCSM â Râ2.3±0.5 at larger radii. We infer that the flat part of the density profile corresponds to a CSM shell with mass âŒ0.021 Mâ, and that the progenitor's effective mass-loss rate varied with time over the range (50â500) Ă 10â5 Mâ yrâ1 for an adopted wind velocity vw = 1000 km sâ1 and shock microphysical parameters epsilone = 0.1, epsilonB = 0.01. These results add to the mounting observational evidence for departures from the traditional single-wind mass-loss scenarios in evolved, massive stars in the centuries leading up to core collapse. Potentially viable scenarios include mass loss powered by gravity waves and/or interaction with a binary companion
Evidence for Extended Hydrogen-Poor CSM in the Three-Peaked Light Curve of Stripped Envelope Ib Supernova
We present multi-band ATLAS photometry for SN 2019tsf, a stripped-envelope
Type Ib supernova (SESN). The SN shows a triple-peaked light curve and a late
(re-)brightening, making it unique among stripped-envelope systems. The
re-brightening observations represent the latest photometric measurements of a
multi-peaked Type Ib SN to date. As late-time photometry and spectroscopy
suggest no hydrogen, the potential circumstellar material (CSM) must be H-poor.
Moreover, late (>150 days) spectra show no signs of narrow emission lines,
further disfavouring CSM interaction. On the contrary, an extended CSM
structure is seen through a follow-up radio campaign with Karl G. Jansky Very
Large Array (VLA), indicating a source of bright optically thick radio emission
at late times, which is highly unusual among H-poor SESNe. We attribute this
phenomenology to an interaction of the supernova ejecta with
spherically-asymmetric CSM, potentially disk-like, and we present several
models that can potentially explain the origin of this rare Type Ib supernova.
The warped disc model paints a novel picture, where the tertiary companion
perturbs the progenitors CSM, that can explain the multi-peaked light curves of
SNe, and here we apply it to SN 2019tsf. This SN 2019tsf is likely a member of
a new sub-class of Type Ib SNe and among the recently discovered class of SNe
that undergo mass transfer at the moment of explosionComment: 23 pages, Comments are welcome, Submitted to Ap
SN 2019ehk: A Double-peaked Ca-rich Transient with Luminous X-Ray Emission and Shock-ionized Spectral Features
We present panchromatic observations and modeling of the Calcium-rich supernova (SN) 2019ehk in the star-forming galaxy M100 (d â 16.2 Mpc) starting 10 hr after explosion and continuing for ~300 days. SN 2019ehk shows a double-peaked optical light curve peaking at t = 3 and 15 days. The first peak is coincident with luminous, rapidly decaying Swift-XRTâdiscovered X-ray emission (L_x â 10âŽÂč erg sâ»Âč at 3 days; L_x â tâ»Âł), and a Shane/Kast spectral detection of narrow Hα and He II emission lines (v â 500 km sâ»Âč) originating from pre-existent circumstellar material (CSM). We attribute this phenomenology to radiation from shock interaction with extended, dense material surrounding the progenitor star at r (0.1â1) Ă 10Âčâ· cm. The photometric and spectroscopic properties during the second light-curve peak are consistent with those of Ca-rich transients (rise-time of t_r = 13.4 ± 0.210 days and a peak B-band magnitude of M_B = â15.1 ± 0.200 mag). We find that SN 2019ehk synthesized (3.1 ± 0.11) Ă 10â»ÂČ M_â of â”â¶Ni and ejected M_(ej) = (0.72 ± 0.040) Mâ total with a kinetic energy E_k = (1.8 ± 0.10) Ă 10â”â° erg. Finally, deep HST pre-explosion imaging at the SN site constrains the parameter space of viable stellar progenitors to massive stars in the lowest mass bin (~10 M_â) in binaries that lost most of their He envelope or white dwarfs (WDs). The explosion and environment properties of SN 2019ehk further restrict the potential WD progenitor systems to low-mass hybrid HeCO WD+CO WD binaries