Multimessenger observations of the neutron star merger GW170817 and its kilonova proved that neutron star mergers can synthesize large quantities of r-process elements. If neutron star mergers in ...fact dominate all r-process element production, then the distribution of kilonova ejecta compositions should match the distribution of r-process abundance patterns observed in stars. The lanthanide fraction (XLa) is a measurable quantity in both kilonovae and metal-poor stars, but it has not previously been explicitly calculated for stars. Here we compute the lanthanide fraction distribution of metal-poor stars (Fe/H < − 2.5) to enable comparison to current and future kilonovae. The full distribution peaks at log XLa ∼ −1.8, but r-process-enhanced stars (Eu/Fe > 0.7) have distinctly higher lanthanide fractions: . We review observations of GW170817 and find general consensus that the total , somewhat lower than the typical metal-poor star and inconsistent with the most highly r-enhanced stars. For neutron star mergers to remain viable as the dominant r-process site, future kilonova observations should be preferentially lanthanide-rich (including a population of ∼10% with ). These high-XLa kilonovae may be fainter and more rapidly evolving than GW170817, posing a challenge for discovery and follow-up observations. Both optical and (mid-)infrared observations will be required to robustly constrain kilonova lanthanide fractions. If such high-XLa kilonovae are not found in the next few years, that likely implies that the stars with the highest r-process enhancements have a different origin for their r-process elements.
Abstract
It is unclear if neutron star mergers can explain the observed
r
-process abundances of metal-poor stars. Collapsars, defined here as rotating massive stars whose collapse results in a ...rapidly accreting disk around a black hole that can launch jets, are a promising alternative. We find that we can produce a self-consistent model in which a population of collapsars with stochastic europium yields synthesizes all of the
r
-process material in metal-poor (Fe/H < − 2.5) stars. Our model reproduces the observed scatter and evolution of scatter of Eu/Fe abundances. We find that if collapsars are the dominant
r
-process site for metal-poor stars,
r
-process synthesis may be linked to supernovae that produce long
γ
-ray bursts. Our results also allow for the possibility that core-collapse supernovae beyond those that launch
γ
-ray bursts also produce
r
-process material (e.g., potentially a subset of Type Ic-BL supernovae). Furthermore, we identify collapsar jet properties (isotropic energy, engine luminosity, or engine time) that may trace
r
-process yield and verify that the amount of
r
-process yield produced per collapsar in our model ( ∼ 0.07
M
⊙
) is consistent with other independent estimates. In the future, achieving 0.05 dex precision on distribution scatter or a reliable selection function would further constrain our probe of
r
-process production. Our model would also hold for another prompt
r
-process site with a power-law yield, and work is needed to determine if, for example, fast-merging neutron stars can also explain abundance scatter.
ABSTRACT
We present Hubble Space Telescope imaging of a pre-explosion counterpart to SN 2019yvr obtained 2.6 yr 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 analysed pre-explosion Spitzer/Infrared Array Camera (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 $E(B-V)=0.51\substack{+0.27\\
-0.16}$ mag for SN 2019yvr. Correcting photometry of the pre-explosion source for dust reddening, we determine that this source is consistent with a log (L/L⊙) = 5.3 ± 0.2 and $T_{\mathrm{eff}} = 6800\substack{+400\\
-200}$ K star. This relatively cool photospheric temperature implies a radius of 320$\substack{+30\\
-50}~\mathrm{ R}_{\odot}$, 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 still seemingly in conflict with the SN Ib classification of SN 2019yvr. SN 2019yvr had signatures of strong circumstellar interaction in late-time (>150 d) 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.
THE YELLOW AND RED SUPERGIANTS OF M33 DROUT, Maria R; MASSEY, Philip; MEYNET, Georges
Astrophysical journal/The Astrophysical journal,
05/2012, Letnik:
750, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Yellow and red supergiants are evolved massive stars whose numbers and locations on the Hertzsprung-Russell (H-R) diagram can provide a stringent test for models of massive star evolution. Previous ...studies have found large discrepancies between the relative number of yellow supergiants (YSGs) observed as a function of mass and those predicted by evolutionary models, while a disagreement between the predicted and observed locations of red supergiants (RSGs) on the H-R diagram was only recently resolved. Here, we extend these studies by examining the YSG and RSG populations of M33. Unfortunately, identifying these stars is difficult as this portion of the color-magnitude diagram is heavily contaminated by foreground dwarfs. We identify the RSGs through a combination of radial velocities and a two-color surface gravity discriminant, and after re-characterizing the rotation curve of M33 with our newly selected RSGs, we identify the YSGs through a combination of radial velocities and the strength of the O I lambda7774 triplet. We examine ~1300 spectra in total and identify 121 YSGs (a sample that is unbiased in luminosity above log(L/L sub(middot in circle)) ~ 4.8) and 189 RSGs. After placing these objects on the H-R diagram, we find that the latest generation of Geneva evolutionary tracks shows excellent agreement with the observed locations of our RSGs and YSGs, the observed relative number of YSGs with mass, and the observed RSG upper mass limit. These models therefore represent a drastic improvement over previous generations.
Abstract
We perform a systematic study of the
56
Ni mass (
M
Ni
) of 27 stripped-envelope supernovae (SESNe) by modeling their light-curve tails, highlighting that use of “Arnett’s rule” ...overestimates
M
Ni
for SESNe by a factor of ∼2. Recently, Khatami & Kasen presented a new model relating the peak time (
t
p
) and luminosity (
L
p
) of a radioactively powered supernova to its
M
Ni
that addresses several limitations of Arnett-like models, but depends on a dimensionless parameter,
β
. Using observed
t
p
,
L
p
, and tail-measured
M
Ni
values for 27 SESNe, we observationally calibrate
β
for the first time. Despite scatter, we demonstrate that the model of Khatami & Kasen with empirically calibrated
β
values provides significantly improved measurements of
M
Ni
when only photospheric data are available. However, these observationally constrained
β
values are systematically lower than those inferred from numerical simulations, primarily because the observed sample has significantly higher (0.2–0.4 dex)
L
p
for a given
M
Ni
. While effects due to composition, mixing, and asymmetry can increase
L
p
none can explain the systematically low
β
values. However, the discrepancy can be alleviated if ∼7%–50% of
L
p
for the observed sample comes from sources other than radioactive decay. Either shock cooling or magnetar spin-down could provide the requisite luminosity. Finally, we find that even with our improved measurements, the
M
Ni
values of SESNe are still a factor of ∼3 larger than those of hydrogen-rich Type II SNe, indicating that these supernovae are inherently different in terms of the initial mass distributions of their progenitors or their explosion mechanisms.
We present detailed optical photometry for 25 Type Ibc supernovae (SNe Ibc) within d 150 Mpc obtained with the robotic Palomar 60 inch telescope in 2004-2007. This study represents the first uniform, ...systematic, and statistical sample of multi-band SNe Ibc light curves available to date. We correct the light curves for host galaxy extinction using a new technique based on the photometric color evolution, namely, we show that the (V -- R) color of extinction-corrected SNe Ibc at Delta *Dt 10 days after V-band maximum is tightly distributed, (V -- R) V10 = 0.26 ? 0.06 mag. Using this technique, we find that SNe Ibc typically suffer from significant host galaxy extinction, E(B -- V) 0.4 mag. A comparison of the extinction-corrected light curves for helium-rich (Type Ib) and helium-poor (Type Ic) SNe reveals that they are statistically indistinguishable, both in luminosity and decline rate. We report peak absolute magnitudes of MR = --17.9 ? 0.9 mag and MR = --18.3 ? 0.6 mag for SNe Ib and Ic, respectively. Focusing on the broad-lined (BL) SNe Ic, we find that they are more luminous than the normal SNe Ibc sample, MR = --19.0 ? 1.1 mag, with a probability of only 1.6% that they are drawn from the same population of explosions. By comparing the peak absolute magnitudes of SNe Ic-BL with those inferred for local engine-driven explosions (GRB-SN 1998bw, XRF-SN 2006aj, and SN 2009bb) we find a 25% probability that relativistic SNe are drawn from the overall SNe Ic-BL population. Finally, we fit analytic models to the light curves to derive typical 56Ni masses of M Ni 0.2 and 0.5 M for SNe Ibc and SNe Ic-BL, respectively. With reasonable assumptions for the photospheric velocities, we further extract kinetic energy and ejecta mass values of M ej 2 M and EK 1051 erg for SNe Ibc, while for SNe Ic-BL we find higher values, M ej 5 M and EK 1052 erg. We discuss the implications for the progenitors of SNe Ibc and their relation to those of engine-driven explosions.
Abstract
Freshly synthesized
r
-process elements in kilonovae ejecta imprint absorption features on optical spectra, as observed in the GW170817 binary neutron star merger. These spectral features ...encode insights into the physical conditions of the
r
-process and the origins of the ejected material, but associating features with particular elements and inferring the resultant abundance pattern is computationally challenging. We introduce Spectroscopic
r
-Process Abundance Retrieval for Kilonovae (
SPARK
), a modular framework to perform Bayesian inference on kilonova spectra with the goals of inferring elemental abundance patterns and identifying absorption features at early times.
SPARK
inputs an atomic line list and abundance patterns from reaction network calculations into the
TARDIS
radiative transfer code. It then performs fast Bayesian inference on observed kilonova spectra by training a Gaussian process surrogate for the approximate posteriors of kilonova ejecta parameters, via active learning. We use the spectrum of GW170817 at 1.4 days to perform the first inference on a kilonova spectrum, and recover a complete abundance pattern. Our inference shows that this ejecta was generated by an
r
-process with either (1) high electron fraction
Y
e
∼ 0.35 and high entropy
s
/
k
B
∼ 25, or, (2) a more moderate
Y
e
∼ 0.30 and
s
/
k
B
∼ 14. These parameters are consistent with a shocked, polar dynamical component, and a viscously driven outflow from a remnant accretion disk, respectively. We also recover previous identifications of strontium absorption at ∼8000 Å, and tentatively identify yttrium and/or zirconium at ≲4500 Å. Our approach will enable computationally tractable inference on the spectra of future kilonovae discovered through multimessenger observations.
We present a wide-field optical imaging search for electromagnetic counterparts to the likely neutron star-black hole (NS-BH) merger GW190814/S190814bv. This compact binary merger was detected ...through gravitational waves by the LIGO/Virgo interferometers, with masses suggestive of an NS-BH merger. We imaged the LIGO/Virgo localization region using the MegaCam instrument on the Canada-France-Hawaii Telescope (CFHT). We describe our hybrid observing strategy of both tiling and galaxy-targeted observations, as well as our image differencing and transient detection pipeline. Our observing campaign produced some of the deepest multiband images of the region between 1.7 and 8.7 days post-merger, reaching a 5 depth of g > 22.8 (AB mag) at 1.7 days and i > 23.1 and i > 23.9 at 3.7 and 8.7 days, respectively. These observations cover a mean total integrated probability of 67.0% of the localization region. We find no compelling candidate transient counterparts to this merger in our images, which suggests that the lighter object was tidally disrupted inside of the BH's innermost stable circular orbit, the transient lies outside of the observed sky footprint, or the lighter object is a low-mass BH. We use 5 source detection upper limits from our images in the NS-BH interpretation of this merger to constrain the mass of the kilonova ejecta to be Mej 0. 015M for a "blue" ( ) kilonova and Mej 0. 04M for a "red" ( ) kilonova. Our observations emphasize the key role of large-aperture telescopes and wide-field imagers such as CFHT MegaCam in enabling deep searches for electromagnetic counterparts to gravitational-wave events.
In the standard view of massive star evolution, luminous blue variables (LBVs) are transitional objects between the most massive O-type stars and Wolf-Rayet (WR) stars. With short lifetimes, these ...stars should all be found near one another. A recent study of LBVs in the Large Magellanic Cloud (LMC) found instead that LBVs are considerably more isolated than either O-type stars or WRs, with a distribution intermediate between that of the WRs and red supergiants (RSGs). A similar study, using a more restricted sample of LBVs, reached the opposite conclusion. Both studies relied upon the distance to the nearest spectroscopically identified O-type star to define the degree of isolation. However, our knowledge of the spectroscopic content of the LMC is quite spotty. Here we re-examine the issue using carefully defined photometric criteria to select the highest-mass unevolved stars ("bright blue stars," or BBSs), using spatially complete photometric catalogs of the LMC, M31, and M33. Our study finds that the LBVs are no more isolated than BBSs or WRs. This result holds no matter which sample of LBVs we employ. A statistical test shows that we can rule out the LBVs having the same distribution as the RSGs, which are about 2× more isolated. We demonstrate the robustness of our results using the second-closest neighbor. Furthermore, the majority of LBVs in the LMC are found in or near OB associations as are the BBS and WRs; the RSGs are not. We conclude that the spatial distribution of LBVs therefore is consistent with the standard picture of massive star evolution.
Abstract
We present preexplosion optical and infrared (IR) imaging at the site of the type II supernova (SN II) 2023ixf in Messier 101 at 6.9 Mpc. We astrometrically registered a ground-based image ...of SN 2023ixf to archival Hubble Space Telescope (HST), Spitzer Space Telescope (Spitzer), and ground-based near-IR images. A single point source is detected at a position consistent with the SN at wavelengths ranging from HST
R
band to Spitzer 4.5
μ
m. Fitting with blackbody and red supergiant (RSG) spectral energy distributions (SEDs), we find that the source is anomalously cool with a significant mid-IR excess. We interpret this SED as reprocessed emission in a 8600
R
⊙
circumstellar shell of dusty material with a mass ∼5 × 10
−5
M
⊙
surrounding a
log
(
L
/
L
⊙
)
=
4.74
±
0.07
and
T
eff
=
3920
−
160
+
200
K RSG. This luminosity is consistent with RSG models of initial mass 11
M
⊙
, depending on assumptions of rotation and overshooting. In addition, the counterpart was significantly variable in preexplosion Spitzer 3.6 and 4.5
μ
m imaging, exhibiting ∼70% variability in both bands correlated across 9 yr and 29 epochs of imaging. The variations appear to have a timescale of 2.8 yr, which is consistent with
κ
-mechanism pulsations observed in RSGs, albeit with a much larger amplitude than RSGs such as
α
Orionis (Betelgeuse).
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