105 research outputs found
Infrared spectroscopy of the merger candidate KIC 9832227
Context. It has been predicted that the object KIC 9832227 – a contact binary star – will undergo a merger in 2022.2±0.7.We describe the near infrared spectrum of this object as an impetus to obtain pre-merger data.
Aims. We aim to characterise (i) the nature of the individual components of the binary and (ii) the likely circumbinary environment, so that the merger – if and when it occurs – can be interpreted in an informed manner.
Methods. We use infrared spectroscopy in the wavelength range 0.7 μm–2.5 μm, to which we fit model atmospheres to represent the individual stars. We use the binary ephemeris to determine the orbital phase at the time of observation.
Results. We find that the infrared spectrum is best fitted by a single component having effective temperature 5 920 K, log [g] = 4.1 and solar metallicity, consistent with the fact that the system was observed at conjunction.
Conclusions. The strength of the infrared H lines is consistent with a high value of log g, and the strength of the Ca ii triplet indicates the presence of a chromosphere, as might be expected from rapid stellar rotation. The He i absorption we observe likely arises in He excited by coronal activity in a circumstellar envelope, suggesting that the weakness of the Ca ii triplet is also likely chromospheric in origin
Flat-topped NIR profiles originating from an unmixed helium shell in the Type IIb SNÂ 2020acat
The Near Infrared (NIR) spectra of the Type IIb supernova (SN IIb) SN 2020acat, obtained at various times throughout the optical follow-up campaign, are presented here. The dominant He i 1.0830 μm and 2.0581 μm features are seen to develop flat-topped P-Cygni profiles as the NIR spectra evolve towards the nebular phase. The nature of the NIR helium peaks imply that there was a lack of mixing between the helium shell and the heavier inner ejecta in SN 2020acat. Analysis of the flat-top features showed that the boundary of the lower velocity of the helium shell was ∼3 − 4 × 103 km s−1. The NIR spectra of SN 2020acat were compared to both SN 2008ax and SN 2011dh to determine the uniqueness of the flat-topped helium features. While SN 2011dh lacked a flat-topped NIR helium profile, SN 2008ax displayed NIR helium features that were very similar to those seen in SN 2020acat, suggesting that the flat-topped feature is not unique to SN 2020acat and may be the product of the progenitors structure
Carnegie Supernova Project-II: The Near-infrared Spectroscopy Program
Shifting the focus of Type Ia supernova (SN Ia) cosmology to the
near-infrared (NIR) is a promising way to significantly reduce the systematic
errors, as the strategy minimizes our reliance on the empirical
width-luminosity relation and uncertain dust laws. Observations in the NIR are
also crucial for our understanding of the origins and evolution of these
events, further improving their cosmological utility. Any future experiments in
the rest-frame NIR will require knowledge of the SN Ia NIR spectroscopic
diversity, which is currently based on a small sample of observed spectra.
Along with the accompanying paper, Phillips et al. (2018), we introduce the
Carnegie Supernova Project-II (CSP-II), to follow up nearby SNe Ia in both the
optical and the NIR. In particular, this paper focuses on the CSP-II NIR
spectroscopy program, describing the survey strategy, instrumental setups, data
reduction, sample characteristics, and future analyses on the data set. In
collaboration with the Harvard-Smithsonian Center for Astrophysics (CfA)
Supernova Group, we obtained 661 NIR spectra of 157 SNe Ia. Within this sample,
451 NIR spectra of 90 SNe Ia have corresponding CSP-II follow-up light curves.
Such a sample will allow detailed studies of the NIR spectroscopic properties
of SNe Ia, providing a different perspective on the properties of the unburned
material, radioactive and stable nickel produced, progenitor magnetic fields,
and searches for possible signatures of companion stars.Comment: 20 pages, 7 figures, accepted for publication in PAS
A Speed Bump: SN 2021aefx Shows that Doppler Shift Alone Can Explain Early Excess Blue Flux in Some Type Ia Supernovae
We present early-time photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2021aefx. The early-time u-band light curve shows an excess flux when compared to normal SNe Ia. We suggest that the early excess blue flux may be due to a rapid change in spectral velocity in the first few days post explosion, produced by the emission of the Ca ii H&K feature passing from the u to the B bands on the timescale of a few days. This effect could be dominant for all SNe Ia that have broad absorption features and early-time velocities over 25,000 km s. It is likely to be one of the main causes of early excess u-band flux in SNe Ia that have early-time high velocities. This effect may also be dominant in the UV filters, as well as in places where the SN spectral energy distribution is quickly rising to longer wavelengths. The rapid change in velocity can only produce a monotonic change (in flux-space) in the u band. For objects that explode at lower velocities, and have a more structured shape in the early excess emission, there must also be an additional parameter producing the early-time diversity. More early-time observations, in particular early spectra, are required to determine how prominent this effect is within SNe Ia.C.A. and B.J.S. are supported by NSF grants AST-1907570, AST-1908952, AST-1920392, and AST-1911074. M.D.S. is funded in part by an Experiment grant (No. 28021) from the Villum FONDEN, and by a project 1 grant (No. 8021-00170B) from the Independent Research Fund Denmark (IRFD). P.H. acknowledges support by National Science Foundation (NSF) grant AST- 1715133. E.B. and J.D. are supported in part by NASA grant 80NSSC20K0538. This work has been generously supported by the National Science Foundation under grants AST-1008343, AST-1613426, AST-1613455, and AST1613472. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at the Las Campanas Observatory, Chile. We would like to thank the technical staff for constant support for observations on the Swope telescope. The early-time spectrum that was critical for this analysis came from SALT through Rutgers University time via program 2021-1-MLT-007 (PI: Jha). L.G. acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, and the European Social Fund (ESF) "Investing in your future" under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, from Centro Superior de Investigaciones CientÃficas (CSIC) under the PIE project 20215AT016, and the program Unidad de Excelencia MarÃa de Maeztu CEX2020-001058-M
Measuring an Off-center Detonation through Infrared Line Profiles: The Peculiar Type Ia Supernova SN 2020qxp/ASASSN-20jq
We present and analyze a near-infrared (NIR) spectrum of the underluminous Type Ia supernova SN 2020qxp/ASASSN-20jq obtained with NIRES at the Keck Observatory, 191 days after B-band maximum. The spectrum is dominated by a number of broad emission features, including the [Fe ii] at 1.644 μm, which is highly asymmetric with a tilted top and a peak redshifted by ≈2000 km s-1. In comparison with 2D non-LTE synthetic spectra computed from 3D simulations of off-center delayed-detonation Chandrasekhar-mass (Mch) white dwarf (WD) models, we find good agreement between the observed lines and the synthetic profiles, and are able to unravel the structure of the progenitor's envelope. We find that the size and tilt of the [Fe ii] 1.644 μm profile (in velocity space) is an effective way to determine the location of an off-center delayed-detonation transition (DDT) and the viewing angle, and it requires a WD with a high central density of ∼4 × 109 g cm-3. We also tentatively identify a stable Ni feature around 1.9 μm characterized by a "pot-belly"profile that is slightly offset with respect to the kinematic center. In the case of SN 2020qxp/ASASSN-20jq, we estimate that the location of the DDT is ∼0.3MWD off center, which gives rise to an asymmetric distribution of the underlying ejecta. We also demonstrate that low-luminosity and high-density WD SN Ia progenitors exhibit a very strong overlap of Ca and 56Ni in physical space. This results in the formation of a prevalent [Ca ii] 0.73 μm emission feature that is sensitive to asymmetry effects. Our findings are discussed within the context of alternative scenarios, including off-center C/O detonations in He-triggered sub-MCh WDs and the direct collision of two WDs. Snapshot programs with Gemini/Keck/Very Large Telescope (VLT)/ELT-class instruments and our spectropolarimetry program are complementary to mid-IR spectra by the James Webb Space Telescope (JWST).P.H., A.F., B.H., D.C., and E.Y.H. acknowledge
support by the National Science Foundation (NSF) grant AST1715133. E.B. was supported in part by NASA grant
80NSSC20K0538. C.A. and B.J.S. are supported by NASA
grant 80NSSC19K1717 and NSF grants AST-1920392 and
AST-1911074. M.S. is supported by grants from the Villum
FONDEN (28021) and the Independent Research Fund Denmark (8021-00170B). M.A.T. acknowledges support from the
DOE CSGF through grant DE-SC0019323. L.G. acknowledges
financial support from the Spanish Ministry of Science,
Innovation and Universities (MICIU) under the 2019 Ramón
y Cajal program RYC2019-027683 and from the Spanish
MICIU project PID2020-115253GA-I00. C.R.B., E.Y.H., M.
M.P., N.B.S. and P.H. are supported by the NSF grant AST1613472
Testing the Homogeneity of Type Ia Supernovae in the Near-Infrared for Accurate Distance Estimations
Type Ia Supernovae (SNe Ia) have been extensively used as standardisable
candles in the optical for several decades. However, SNe Ia have shown to be
more homogeneous in the near-infrared (NIR), where the effect of dust
extinction is also attenuated. In this work, we explore the possibility of
using a low number of NIR observations for accurate distance estimations, given
the homogeneity at these wavelengths. We found that one epoch in and/or
band, plus good -band coverage, gives an accurate estimation of peak
magnitudes in () and () bands. The use of a single
NIR epoch only introduces an additional scatter of mag for epochs
around the time of -band peak magnitude (). We also tested the
effect of optical cadence and signal-to-noise ratio (S/N) in the estimation of
and its uncertainty propagation to the NIR peak magnitudes. Both
cadence and S/N have a similar contribution, where we constrained the
introduced scatter of each to mag in and in
. However, these effects are expected to be negligible, provided the
data quality is comparable to that obtained for observations of nearby SNe
(). The effect of S/N in the NIR was tested as well. For SNe Ia
at , NIR observations with better S/N than that found in the
CSP sample is necessary to constrain the introduced scatter to a minimum
( mag). These results provide confidence for our FLOWS project
that aims in using SNe Ia with public ZTF optical light curves and few NIR
epochs to map out the peculiar velocity field of the local Universe. This will
allow us to determine the distribution of dark matter in our own supercluster,
Laniakea, and test the standard cosmological model by measuring the growth rate
of structures, parameterised by , and the Hubble-Lema\^itre constant,
.Comment: Accepted in A&
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