We present initial results from a time series BVI survey of two fields in NGC 4258 using the HST ACS. This galaxy was selected because of its accurate maser-based distance, which is anticipated to ...have a total uncertainty of 63%. The goal of the HST observations is to provide an absolute calibration of the Cepheid distance scale and to measure its dependence on chemical abundance (the so-called metallicity effect). We carried out observations of two fields at different galactocentric distances with a mean abundance difference of 0.5 dex. We discovered a total of 281 Cepheids with periods ranging from 4 to 45 days (the duration of our observing window). We determine a Cepheid distance modulus for NGC 4258 (relative to the LMC) of mu sub(0) = 10.88 c 0.04 (random) c 0.05 (systematic) mag. Given the published maser distance to the galaxy, this implies k sub(0)(LMC) = 18.41 c 0.10 sub(r) c 0.13 sub(s) mag or D(LMC) = 48.1 c 2.3 sub(r) c 2.9 sub(s) kpc. We measure a metallicity effect of g = -0.29 c 0.09 sub(r) c 0.05 sub(s) mag dex super(-1). We see no evidence for a variation in the slope of the period-luminosity relation as a function of abundance. We estimate a Hubble constant of H sub(0) = 74 c 3 sub(r) c 6 sub(s) km s super(-1) Mpc super(-1) using a recent sample of four well-observed Type Ia SNe and our new calibration of the Cepheid distance scale. It may soon be possible to measure the value of H sub(0) with a total uncertainty of 5%, with consequent improvement in the determination of the equation of state of dark energy.
The luminous Type IIn Supernova (SN) 2010jl shows strong evidence for the interaction of the SN ejecta with dense circumstellar material (CSM). We present observations of SN 2010jl for t ∼ 900 d ...after its earliest detection, including a sequence of optical spectra ranging from t = 55 to 909 d. We also supplement our late time spectra and the photometric measurements in the literature with an additional epoch of new, late time BVRI photometry. Combining available photometric and spectroscopic data, we derive a semi-bolometric optical light curve and calculate a total radiated energy in the optical for SN 2010jl of ∼3.5 × 1050 erg, confirming the result of Fransson et al. We also examine the evolution of the Hα emission line profile in detail and find evidence for asymmetry in the profile for t ≳ 775 d that is not easily explained by any of the proposed scenarios for this fascinating event. Finally, we discuss the interpretations from the literature of the optical and near-infrared light curves, and propose that the most likely explanation of their evolution is the formation of new dust in the dense, pre-existing CSM wind after ∼300 d.
OBSERVING THE NEXT GALACTIC SUPERNOVA Adams, Scott M; Kochanek, C S; Beacom, John F ...
The Astrophysical journal,
12/2013, Letnik:
778, Številka:
2
Journal Article
Recenzirano
Odprti dostop
No supernova (SN) in the Milky Way has been observed since the invention of the optical telescope, instruments for other wavelengths, neutrino detectors, or gravitational wave observatories. It would ...be a tragedy to miss the opportunity to fully characterize the next one. To aid preparations for its observations, we model the distance, extinction, and magnitude probability distributions of a successful Galactic core-collapse supernova (ccSN), its shock breakout radiation, and its massive star progenitor. We find that shock breakouts from failed ccSNe of red supergiants may be more observable than those of successful SNe due to their lower radiation temperatures. Based on our modeled observability, we find a Galactic ccSN rate of 3.2 super(+7.3) sub(-2.6) per century and a Galactic SN Ia rate of 1.4 super(+1.4) sub(-0.8) per century for a total Galactic SN rate of 4.6 super(+7.4) sub(-2.7) per century is needed to account for the SNe observed over the last millennium, which implies a Galactic star formation rate of 3.6 super(+8.3) sub(-3.0) M sub(middot in circle) yr super(-1).
Abstract
We report comprehensive multi-wavelength observations of a peculiar Type Ia-like supernova (“SN Ia-pec”) ASASSN-15pz. ASASSN-15pz is a spectroscopic “twin” of SN 2009dc, a so-called ...“Super-Chandrasekhar-mass” SN, throughout its evolution, but it has a peak luminosity
that is
dimmer and comparable to the SN 1991T sub-class of SNe Ia at the luminous end of the normal width-luminosity relation. The synthesized
56
Ni mass of
is also substantially less than that found for several 2009dc-like SNe. Previous well-studied 2009dc-like SNe have generally suffered from large and uncertain amounts of host-galaxy extinction, which is negligible for ASASSN-15pz. Based on the color of ASASSN-15pz, we estimate a host extinction for SN 2009dc of
and confirm its high luminosity (
). The 2009dc-like SN population, which represents ∼1% of SNe Ia, exhibits a range of peak luminosities, and do not fit onto the tight width-luminosity relation. Their optical light curves also show significant diversity of late-time (≳50 days) decline rates. The nebular-phase spectra provide powerful diagnostics to identify the 2009dc-like events as a distinct class of SNe Ia. We suggest referring to these sources using the phenomenology-based “2009dc-like SN Ia-pec” instead of “Super-Chandrasekhar SN Ia,” which is based on an uncertain theoretical interpretation.
First Resolution of Microlensed Images Dong, Subo; Mérand, A.; Delplancke-Ströbele, F. ...
The Astrophysical journal,
01/2019, Letnik:
871, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
We employ Very Large Telescope Interferometer GRAVITY to resolve, for the first time, the two images generated by a gravitational microlens. The measurements of the image separation
mas, and ...hence the Einstein radius
θ
E
= 1.87 ± 0.03 mas, are precise. This demonstrates the robustness of the method, provided that the source is bright enough for GRAVITY (
K
≲ 10.5) and the image separation is of order of or larger than the fringe spacing. When
θ
E
is combined with a measurement of the “microlens parallax”
, the two will together yield the lens mass and lens–source relative parallax and proper motion. Because the source parallax and proper motion are well measured by
Gaia
, this means that the lens characteristics will be fully determined, whether or not it proves to be luminous. This method can be a powerful probe of dark, isolated objects, which are otherwise quite difficult to identify, much less characterize. Our measurement contradicts Einstein’s prediction that “the luminous circle i.e., microlensed image cannot be distinguished” from a star.
The Largest M Dwarf Flares from ASAS-SN Schmidt, Sarah J.; Shappee, Benjamin J.; van Saders, Jennifer L. ...
The Astrophysical journal,
05/2019, Letnik:
876, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The All-sky Automated Survey for Supernovae (ASAS-SN) is the only project in existence to scan the entire sky in optical light approximately every day, reaching a depth of g ∼ 18 mag. Over the course ...of its first 4 yr of transient alerts (2013-2016), ASAS-SN observed 53 events classified as likely M dwarf flares. We present follow-up photometry and spectroscopy of all 53 candidates, confirming flare events on 47 M dwarfs, one K dwarf, and one L dwarf. The remaining four objects include a previously identified T Tauri star, a young star with outbursts, and two objects too faint to confirm. A detailed examination of the 49 flare star light curves revealed an additional six flares on five stars, resulting in a total of 55 flares on 49 objects ranging in V-band contrast from ΔV = −1 to −10.2 mag. Using an empirical flare model to estimate the unobserved portions of the flare light curve, we obtain lower limits on the V-band energy emitted during each flare, spanning -35, which are among the most energetic flares detected on M dwarfs. The ASAS-SN M dwarf flare stars show a higher fraction of H emission, as well as stronger H emission, compared to M dwarfs selected without reference to activity, consistent with belonging to a population of more magnetically active stars. We also examined the distribution of tangential velocities, finding that the ASAS-SN flaring M dwarfs are likely to be members of the thin disk and are neither particularly young nor old.
ASASSN-15lh: A highly super-luminous supernova Dong, Subo; Shappee, B. J.; Prieto, J. L. ...
Science (American Association for the Advancement of Science),
01/2016, Letnik:
351, Številka:
6270
Journal Article
Recenzirano
Odprti dostop
We report the discovery of ASASSN-15lh (SN 2015L), which we interpret as the most luminous supernova yet found. At redshift z = 0.2326, ASASSN-15lh reached an absolute magnitude of Mu,AB = −23.5 ± ...0.1 and bolometric luminosity Lbol = (2.2 ± 0.2) × 10⁴⁵ ergs s⁻¹, which is more than twice as luminous as any previously known supernova. It has several major features characteristic of the hydrogen-poor super-luminous supernovae (SLSNe-l), whose energy sources and progenitors are currently poorly understood. In contrast to most previously known SLSNe-l that reside in star-forming dwarf galaxies, ASASSN-15lh appears to be hosted by a luminous galaxy (MK ≈ −25.5) with little star formation. In the 4 months since first detection, ASASSN-15lh radiated (1.1 ± 0.2) × 10⁵² ergs, challenging the magnetar model for its engine.
ABSTRACT
The scaling of the specific Type Ia supernova (SN Ia) rate with host galaxy stellar mass $\dot{\text{N}}_\text{Ia} / \text{M}_\star \sim \text{M}_\star ^{-0.3}$ as measured in ASAS-SN and ...DES strongly suggests that the number of SNe Ia produced by a stellar population depends inversely on its metallicity. We estimate the strength of the required metallicity dependence by combining the average star formation histories (SFHs) of galaxies as a function of their stellar mass with the mass–metallicity relation (MZR) for galaxies and common parametrizations for the SN Ia delay-time distribution. The differences in SFHs can account for only ∼30 per cent of the increase in the specific SN Ia rate between stellar masses of M⋆ = 1010 and 107.2 M⊙. We find that an additional metallicity dependence of approximately ∼Z−0.5 is required to explain the observed scaling. This scaling matches the metallicity dependence of the close binary fraction observed in APOGEE, suggesting that the enhanced SN Ia rate in low-mass galaxies can be explained by a combination of their more extended SFHs and a higher binary fraction due to their lower metallicities. Due to the shape of the MZR, only galaxies below M⋆ ≈ 3 × 109 M⊙ are significantly affected by the metallicity-dependent SN Ia rates. The $\dot{\text{N}}_\text{Ia} / \text{M}_\star \sim \text{M}_\star ^{-0.3}$ scaling becomes shallower with increasing redshift, dropping by factor of ∼2 at 107.2 M⊙ between z = 0 and 1 with our ∼Z−0.5 scaling. With metallicity-independent rates, this decrease is a factor of ∼3. We discuss the implications of metallicity-dependent SN Ia rates for one-zone models of galactic chemical evolution.
ABSTRACT
Gaia Data Release 3 (DR3) provides >181 000 radial velocity (RV) solutions for single-lined spectroscopic binaries (SB1s) that can be used to search for non-interacting compact object + star ...binary candidates by selecting systems with large mass functions. We selected 234 such systems and identified 115 systems with good RV solutions in DR3. We used light curves from the All-Sky Automated Survey for SuperNovae (ASAS-SN) and the Transiting Exoplanet Survey Satellite (TESS) to identify and remove 31 eclipsing binaries to produce a catalogue of 80 compact object + star candidates, including 38 ellipsoidal variables. The positions of these candidates on Gaia and Two Micron All-Sky Survey (2MASS) colour–magnitude diagrams (CMDs) suggest that many of these systems are binaries with luminous companions. We compared the periods and eccentricities of detached eclipsing binaries in Gaia DR3 and ASAS-SN, and found that ${\sim }11 {{\ \rm per\ cent}}$ and ${\sim }60 {{\ \rm per\ cent}}$ of the binaries had different periods and eccentricities. We also compared RV solutions for 311 binaries in both Gaia DR3 and the Ninth Catalogue of Spectroscopic Binary Orbits (SB9), and found similar results. We do not identify any strong candidates for non-interacting compact object + star binaries.
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