arXiv subjects

J. J. Eldridge

Publications and source records attributed to J. J. Eldridge.

At least 91 records · Page 5Linked to original sources

arXiv2015

Stellar Population Effects on the Inferred Photon Density at Reionization

The relationship between stellar populations and the ionizing flux with which they irradiate their surroundings has profound implications for the evolution of the intergalactic medium. We quantify the ionizing flux arising from synthetic stellar populations which incorporate the evolution of interacting binary stars. We determine that these show ionizing flux boosted by 60 per cent at 0.05 < Z < 0.3 Z_sun and a more modest 10-20 per cent at near-Solar metallicities relative to star-forming populations in which stars evolve in isolation. The relation of ionizing flux to observables such as 1500A continuum and ultraviolet spectral slope is sensitive to attributes of the stellar population including age, star formation history and initial mass function. For a galaxy forming 1 M_sun yr^{-1}, observed at > 100 Myr after the onset of star formation, we predict a production rate of photons capable of ionizing hydrogen, N_ion = 1.4 x 10^{53} s^{-1} at Z = Z_sun and 3.5 x 10^{53} s^{-1} at 0.1 Z_sun, assuming a Salpeter-like initial mass function. We evaluate the impact of these issues on the ionization of the intergalactic medium, finding that the known galaxy populations can maintain the ionization state of the Universe back to z ~ 9, assuming that their luminosity functions continue to M_UV = -10, and that constraints on the intergalactic medium at z ~ 2 - 5 can be satisfied with modest Lyman continuum photon escape fractions of 4 - 24 per cent depending on assumed metallicity.

astro-ph.GA↗

arXiv2015

Did the progenitor of SN2011dh have a binary companion?

We present late-time Hubble Space Telescope (HST) ultraviolet (UV) and optical observations of the site of SN 2011dh in the galaxy M51, ~1164 days post-explosion. At the SN location, we observe a point source that is visible at all wavelengths, that is significantly fainter than the spectral energy distribution (SED) of the Yellow Supergiant progenitor observed prior to explosion. The previously reported photometry of the progenitor is, therefore, completely unaffected by any sources that may persist at the SN location after explosion. In comparison with the previously reported late-time photometric evolution of SN 2011dh, we find that the light curve has plateaued at all wavelengths. The SED of the late-time source is clearly inconsistent with a SED of stellar origin. Although the SED is bright at UV wavelengths, there is no strong evidence that the late-time luminosity originates solely from a stellar source corresponding to the binary companion, although a partial contribution to the observed UV flux from a companion star can not be ruled out.

astro-ph.SR↗

arXiv2015

A Turnoff Detached Binary Star V568 Lyr in the Kepler Field of the Oldest Open Cluster (NGC 6791) in the Galaxy

We present the Kepler photometric light-variation analysis of the late-type double-lined binary system V568 Lyr that is in the field of the high metallicity old open cluster NGC 6791. The radial velocity and the high-quality short-cadence light curve of the system are analysed simultaneously. The masses, radii and luminosities of the component stars are $M_1 = 1.0886\pm0.0031\, M{\odot}$, $M_2 = 0.8292 \pm 0.0026\, M{\odot}$, $R_1 = 1.4203\pm 0.0058\, R{\odot}$, $R_2 = 0.7997 \pm 0.0015\, R{\odot}$, $L_1 = 1.85\pm 0.15\, L{\odot}$, $L_2 = 0.292 \pm 0.018\, L{\odot}$ and their separation is $a = 31.060 \pm 0.002\, R{\odot}$. The distance to NGC 6791 is determined to be $4.260\pm 0.290\,$kpc by analysis of this binary system. We fit the components of this well-detached binary system with evolution models made with the Cambridge STARS and TWIN codes to test low-mass binary star evolution. We find a good fit with a metallicity of $Z = 0.04$ and an age of $7.704\,$Gyr. The standard tidal dissipation, included in TWIN is insufficient to arrive at the observed circular orbit unless it formed rather circular to begin with.

astro-ph.SR↗

arXiv2015

Core-Collapse Supernova Rate Synthesis Within 11 Mpc

The 11 Mpc H-alpha and Ultraviolet Galaxy (11HUGS) Survey traces the star formation activity of nearby galaxies. In addition within this volume the detection completeness of core-collapse supernovae (CCSNe) is high therefore by comparing these observed stellar births and deaths we can make a sensitive test of our understanding of how stars live and die. In this paper, we use the results of the Binary Population and Spectral Synthesis (BPASS) code to simulate the 11HUGS galaxies H-alpha and far-ultraviolet (FUV) star formation rate indicators (SFRIs) and simultaneously match the core-collapse supernova (CCSN) rate. We find that stellar population including interacting binary stars makes little difference to the total CCSN rate but increases the H-alpha and FUV fluxes for a constant number of stars being formed. In addition they significantly increase the predicted rate of type Ibc supernovae (SNe) relative to type II SNe to the level observed in the 11HUGS galaxies. We also find that instead of assuming a constant star formation history (SFH) for the galaxies our best fitting models have a star formation rate (SFR) that peaked more than 3 Myrs ago.

astro-ph.GA↗

arXiv2015

On the Blue Loops of Intermediate-Mass Stars

We consider the blue loops in the Hertzsprung-Russell diagram that occur when intermediate-mass stars begin core helium burning. It has long been known that the excess of helium above the burning shell, the result of the contraction of the convective core during core hydrogen burning, has the effect of making such stars redder and larger than they would be otherwise. The outward motion of the burning shell in mass removes this excess and triggers the loop. Hitherto nobody has attempted to demonstrate why the excess helium has this effect. We consider the effect of the local opacity, which is reduced by excess helium, the shell fuel supply, which is also reduced, and the local mean molecular weight, which is increased. We demonstrate that the mean molecular weight is the decisive reddening factor. The opacity has a much smaller effect and a reduced fuel supply actually favours blueward motion.

astro-ph.SR↗

arXiv2014

Interpreting high [O III]/Hbeta ratios with maturing starbursts

Star forming galaxies at high redshift show ubiquitously high ionization parameters, as measured by the ratio of optical emission lines. We demonstrate that local (z < 0.2) sources selected as Lyman break analogues also manifest high line ratios with a typical [O III]/H beta = 3.36(+0.14,-0.04) - comparable to all but the highest ratios seen in star forming galaxies at z ~ 2-4. We argue that the stellar population synthesis code BPASS can explain the high ionization parameters required through the ageing of rapidly formed star populations, without invoking any AGN contribution. Binary stellar evolution pathways prolong the age interval over which a starburst is likely to show elevated line ratios, relative to those predicted by single stellar evolution codes. As a result, model galaxies at near-Solar metallicities and with ages of up to ~100 Myr after a starburst typically have a line ratio [O III]/H beta~3, consistent with those seen in Lyman break galaxies and local sources with similar star formation densities. This emphasises the importance of including binary evolution pathways when simulating the nebular line emission of young or bursty stellar populations.

astro-ph.GA↗

arXiv2014

Possible binary progenitors for the type Ib supernova iPTF13bvn

Cao et al. (2013) reported a possible progenitor detection for the type Ib supernovae iPTF13bvn for the first time. We find that the progenitor is in fact brighter than the magnitudes previously reported by approximately 0.7 to 0.2 mag with a larger error in the bluer filters. We compare our new magnitudes to our large set of binary evolution models and find that many binary models with initial masses in the range of 10 to 20M(Sun) match this new photometry and other constraints suggested from analysing the supernova. In addition these lower mass stars retain more helium at the end of the model evolution indicating that they are likely to be observed as type Ib supernovae rather than their more massive, Wolf-Rayet counter parts. We are able to rule out typical Wolf-Rayet models as the progenitor because their ejecta masses are too high and they do not fit the observed SED unless they have a massive companion which is the observed source at the supernova location. Therefore only late-time observations of the location will truly confirm if the progenitor was a helium giant and not a Wolf-Rayet star.

astro-ph.SR↗

arXiv2013

A new precise mass for the progenitor of the Type IIP SN 2008bk

The progenitor of the Type IIP SN 2008bk was discovered in pre-explosion g'r'i'IYJHKs images, acquired with European Southern Observatory Very Large Telescope FORS, HAWK-I and ISAAC instruments and the Gemini GMOS-S instrument. The wealth of pre-explosion observations makes the progenitor of this SN one of the best studied, since the detection of the progenitor of SN1987A. Previous analyses of the properties of the progenitor were hampered by the limited quality of the photometric calibration of the pre-explosion images and the crowded nature of the field containing the SN. We present new late-time observations of the site of SN2008bk acquired with identical instrument and filter configurations as the pre-explosion observations, and confirm that the previously identified red supergiant star was the progenitor of this SN and has now disappeared. Image subtraction techniques were used to conduct precise photometry of the now missing progenitor, independently of blending from any nearby stars. The nature of the surrounding stellar population and their contribution to the flux attributed to the progenitor in the pre-explosion images are probed using HST WFC3 UVIS/IR observations. In comparison with MARCS synthetic spectra, we find the progenitor was a highly reddened RSG with luminosity log (L/Lsun)=4.84+/-0.11, corresponding to an initial mass of Minit=12.9+/-1.7Msun. The temperature of the progenitor was hotter than previously expected for RSGs (T ~ 4330K), but consistent with new temperatures derived for RSGs using SED fitting techniques. We show that there is evidence for significant extinction of the progenitor, possibly arising in the CSM; but that this dust yields a similar reddening law to dust found in the ISM (E(B-V)=0.77 with Rv=3.1). [Abridged]

astro-ph.SR↗

arXiv2013

A transdimensional Bayesian method to infer the star formation history of resolved stellar populations

We propose a new method to infer the star formation histories of resolved stellar populations. With photometry one may plot observed stars on a colour-magnitude diagram (CMD) and then compare with synthetic CMDs representing different star formation histories. This has been accomplished hitherto by parametrising the model star formation history as a histogram, usually with the bin widths set by fixed increases in the logarithm of time. A best fit is then found with maximum likelihood methods and we consider the different means by which a likelihood can be calculated. We then apply Bayesian methods by parametrising the star formation history as an unknown number of Gaussian bursts with unknown parameters. This parametrisation automatically provides a smooth function of time. A Reversal Jump Markov Chain Monte Carlo method is then used to find both the most appropriate number of Gaussians, thus avoiding avoid overfitting, and the posterior probability distribution of the star formation rate. We apply our method to artificial populations and to observed data. We discuss the other advantages of the method: direct comparison of different parametrisations and the ability to calculate the probability that a given star is from a given Gaussian. This allows the investigation of possible sub-populations.

astro-ph.SR↗

arXiv2012

On how leakage can affect the Star Formation Rate estimation using Halpha luminosity

We present observational evidence that leakage of ionising photons from star-forming regions can affect the quantification of the star formation rate (SFR) in galaxies. This effect could partially explain the differences between the SFR estimates using the far ultraviolet (FUV) and the Halpha emission. We find that leakage could decrease the SFR(Ha)/SFR(FUV) ratio by up to a 25 per cent. The evidence is based on the observation that the SFR(Ha)/SFR(FUV) ratio is lower for objects showing a shell Halpha structure than for regions exhibiting a much more compact morphology. The study has been performed on three object samples: low luminosity dwarf galaxies from the Local Volume Legacy survey and star-forming regions in the Large Magellanic Cloud and the nearby Local Group galaxy M33. For the three samples we find differences (1.1-1.4sigma) between the SFR(Ha)/SFR(FUV) for compact and shell objects. Although leakage cannot entirely explain the observed trend of SFR(Ha)/SFR(FUV) ratios for systems with low SFR, we show the mechanism can lead to different SFR estimates when using Halpha and FUV luminosities. Therefore, further study is needed to constrain the contribution of leakage to the low SFR(Ha)/SFR(FUV) ratios observed in dwarf galaxies and its impact on the Halpha flux as a SFR indicator in such objects.

astro-ph.CO↗

arXiv2012

Red and dead: The progenitor of SN 2012aw in M95

Core-collapse supernovae (SNe) are the spectacular finale to massive stellar evolution. In this Letter, we identify a progenitor for the nearby core-collapse SN 2012aw in both ground based near-infrared, and space based optical pre-explosion imaging. The SN itself appears to be a normal Type II Plateau event, reaching a bolometric luminosity of 10$^{42}$ erg s$^{-1}$ and photospheric velocities of $\sim$11,000 \kms\ from the position of the H$β$ P-Cygni minimum in the early SN spectra. We use an adaptive optics image to show that the SN is coincident to within 27 mas with a faint, red source in pre-explosion HST+WFPC2, VLT+ISAAC and NTT+SOFI images. The source has magnitudes $F555W$=26.70$\pm$0.06, $F814W$=23.39$\pm$0.02, $J$=21.1$\pm$0.2, $K$=19.1$\pm$0.4, which when compared to a grid of stellar models best matches a red supergiant. Interestingly, the spectral energy distribution of the progenitor also implies an extinction of $A_V>$1.2 mag, whereas the SN itself does not appear to be significantly extinguished. We interpret this as evidence for the destruction of dust in the SN explosion. The progenitor candidate has a luminosity between 5.0 and 5.6 log L/\lsun, corresponding to a ZAMS mass between 14 and 26 \msun\ (depending on $A_V$), which would make this one of the most massive progenitors found for a core-collapse SN to date.

astro-ph.CO↗

arXiv2011

SN 2009md: Another faint supernova from a low mass progenitor

We present adaptive optics imaging of the core collapse supernova (SN) 2009md, which we use together with archival \emph{Hubble Space Telescope} data to identify a coincident progenitor candidate. We find the progenitor to have an absolute magnitude of $V = -4.63^{+0.3}_{-0.4}$ mag and a colour of $V-I = 2.29^{+0.25}_{-0.39}$ mag, corresponding to a progenitor luminosity of log $L$/L$_{\odot}$ $\sim4.54\pm0.19$ dex. Using the stellar evolution code STARS, we find this to be consistent with a red supergiant progenitor with $M = 8.5_{-1.5}^{+6.5}$ M$_{\odot}$. The photometric and spectroscopic evolution of SN 2009md is similar to that of the class of sub-luminous Type IIP SNe; in this paper we compare the evolution of SN 2009md primarily to that of the sub-luminous SN 2005cs. We estimate the mass of $^{56}$Ni ejected in the explosion to be $(5.4\pm1.3) \times 10^{-3}$ M$_{\odot}$\ from the luminosity on the radioactive tail, which is in agreement with the low $^{56}$Ni masses estimated for other sub-luminous Type IIP SNe. From the lightcurve and spectra, we show the SN explosion had a lower energy and ejecta mass than the normal Type IIP SN 1999em. We discuss problems with stellar evolutionary models, and the discrepancy between low observed progenitor luminosities (log $L$/L$_{\odot}$ $\sim4.3-5$ dex) and model luminosities after the second-dredge-up for stars in this mass range, and consider an enhanced carbon burning rate as a possible solution. In conclusion, SN 2009md is a faint SN arising from the collapse of a progenitor close to the lower mass limit for core-collapse. This is now the third discovery of a low mass progenitor star producing a low energy explosion and low $^{56}$Ni ejected mass, which indicates that such events arise from the lowest end of the mass range that produces a core-collapse supernova (7-8 M$_{\odot}$).

astro-ph.SR↗

arXiv2011

Resolved photometry of extragalactic young massive star clusters

We present colour-magnitude diagrams (CMDs) for a sample of seven young massive clusters in the galaxies NGC 1313, NGC 1569, NGC 1705, NGC 5236 and NGC 7793. The clusters have ages in the range 5-50 million years and masses of 10^5 -10^6 Msun. Although crowding prevents us from obtaining photometry in the central regions of the clusters, we are still able to measure up to 30-100 supergiant stars in each of the richest clusters, along with the brighter main sequence stars. The resulting CMDs and luminosity functions are compared with photometry of artificially generated clusters, designed to reproduce the photometric errors and completeness as realistically as possible. In agreement with previous studies, our CMDs show no clear gap between the H-burning main sequence and the He-burning supergiant stars, contrary to predictions by common stellar isochrones. In general, the isochrones also fail to match the observed number ratios of red-to-blue supergiant stars, although the difficulty of separating blue supergiants from the main sequence complicates this comparison. In several cases we observe a large spread (1-2 mag) in the luminosities of the supergiant stars that cannot be accounted for by observational errors. This spread can be reproduced by including an age spread of 10-30 million years in the models. However, age spreads cannot fully account for the observed morphology of the CMDs and other processes, such as the evolution of interacting binary stars, may also play a role.

astro-ph.GA↗

arXiv2011

Binary progenitor models of type IIb supernovae

Massive stars that lose their hydrogen-rich envelope down to a few tenths of a solar mass explode as extended type IIb supernovae, an intriguing subtype that links the hydrogen-rich type II supernovae with the hydrogen-poor type Ib and Ic. The progenitors may be very massive single stars that lose their envelope due to their stellar wind, but mass stripping due to interaction with a companion star in a binary system is currently considered to be the dominant formation channel. We computed an extensive grid of binary models with the Eggleton binary evolution code. The predicted rate from our standard models, which assume conservative mass transfer, is about 6 times smaller than the current rate indicated by observations. It is larger but still comparable to the rate expected from single stars. To recover the observed rate we must generously allow for uncertainties and low accretion efficiencies in combination with limited angular momentum loss from the system. Motivated by the claims of detection and non-detection of companions for a few IIb supernovae, we investigate the properties of the secondary star at the moment of explosion. We identify three cases: (1) the companion appears as a hot O star in about 90% of the cases, (2) the companion becomes an over-luminous B star in about 3% of the cases, or (3) the companion will appear as a K supergiant. The second case, which applies to the well-studied case of SN 1993J and possibly to SN 2001ig, is the least common case and requires that the companion very efficiently accretes the transferred material -in contrast to what is required to recover the overall IIb rate. The fast increasing number of type IIb detections may lead to more solid constraints on model uncertainties, like stellar wind-mass loss and internal mixing.

astro-ph.SR↗

arXiv2010

On the nature of the progenitors of three type II-P supernovae: 2004et, 2006my and 2006ov

The pre-explosion observations of the type II-P supernovae 2006my, 2006ov and 2004et, are re-analysed. In the cases of supernovae 2006my and 2006ov we argue that the published candidate progenitors are not coincident with their respective supernova sites in pre-explosion Hubble Space Telescope observations. We therefore derive upper luminosity and mass limits for the unseen progenitors of both these supernovae, assuming they are red supergiants: 2006my (log L/Lsun = 4.51; mass < 13Msun) and 2006ov (log L/Lsun = 4.29; mass < 10Msun). In the case of supernova 2004et we show that the yellow-supergiant progenitor candidate, originally identified in Canada France Hawaii Telescope images, is still visible ~3 years post-explosion in observations from the William Herschel Telescope. High-resolution Hubble Space Telescope and Gemini (North) adaptive optics late-time imagery reveal that this source is not a single yellow supergiant star, but rather is resolved into at least three distinct sources. We report the discovery of the unresolved progenitor as an excess of flux in pre-explosion Isaac Newton Telescope i'-band imaging. Accounting for the late-time contribution of the supernova using published optical spectra, we calculate the progenitor photometry as the difference between the pre- and post-explosion, ground-based observations. We find the progenitor was most likely a late K to late M-type supergiant of 8 +5/-1 Msun. In all cases we conclude that future, high-resolution observations of the supernova sites will be required to confirm these results.

astro-ph.CO↗

arXiv2009

The death of massive stars - I. Observational constraints on the progenitors of type II-P supernovae

We present the results of a 10.5 yr, volume limited (28 Mpc) search for supernova (SN) progenitor stars. We compile all SNe discovered within this volume (132, of which 27% are type Ia) and determine the relative rates of each sub-type from literature studies : II-P (59%), Ib/c (29%), IIb (5%), IIn (4%) and II-L (3%). Twenty II-P SNe have high quality optical or near-IR pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies (distance, metallicity and extinction) and determine masses and upper mass estimates using the STARS stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a type II-P to form is m(min)=8.5 +1/-1.5 Msol and the maximum mass for II-P progenitors is m(max)=16.5 +/- 1.5 Msol, assuming a Salpeter initial mass function (in the range Gamma = -1.35 +0.3/-0.7). The minimum mass is consistent with current estimates for white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations. Red supergiants in the Local Group have masses up to 25Msol and the minimum mass to produce a Wolf-Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25-30 Msol. We term this discrepancy the "red supergiant problem" and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. Low luminosity SNe with low 56Ni production seem to arise from explosions of low mass progenitors near the mass threshold for core-collapse. (abridged).

astro-ph↗

arXiv2008

VLT detection of a red supergiant progenitor of the type IIP supernova 2008bk

We report the identification of a source coincident with the position of the nearby type II-P supernova (SN) 2008bk in high quality optical and near-infrared pre-explosion images from the ESO Very Large Telescope (VLT). The SN position in the optical and near-infrared pre-explosion images is identified to within about +-70 and +-40 mas, respectively, using post-explosion Ks-band images obtained with the NAOS CONICA adaptive optics system on the VLT. The pre-explosion source detected in four different bands is precisely coincident with SN 2008bk and is consistent with being dominated by a single point source. We determine the nature of the point source using the STARS stellar evolutionary models and find that its colours and luminosity are consistent with the source being a red supergiant progenitor of SN 2008bk with an initial mass of 8.5 +- 1.0 Msun.

astro-ph↗

arXiv2008

The type IIb SN 2008ax: the nature of the progenitor

A source coincident with the position of the type IIb supernova (SN) 2008ax is identified in pre-explosion Hubble Space Telescope (HST) Wide Field Planetary Camera 2 observations in three optical filters. We identify and constrain two possible progenitor systems: (i) a single massive star that lost most of its hydrogen envelope through radiatively driven mass loss processes, prior to exploding as a helium-rich Wolf-Rayet star with a residual hydrogen envelope, and (ii) an interacting binary in a low mass cluster producing a stripped progenitor. Late time, high resolution observations along with detailed modelling of the SN will be required to reveal the true nature of this progenitor star.

astro-ph↗