Riess, Adam (JHU & STScI, USA) [26 May, 11:00]
Refining the Hubble Constant with Parallax, Cepheids and Supernovae
The Hubble constant remains one of the most important parameters in the cosmological model, setting the size and age scales of the Universe. Present uncertainties in the cosmological model including the nature of dark energy, the properties of neutrinos and the scale of departures from flat geometry can be constrained by measurements of the Hubble constant made to higher precision than was possible with the first generations of Hubble Telescope instruments. Streamlined distances ladders constructed from infrared observations of Cepheids and type Ia supernovae with ruthless attention paid to systematics now provide 3.5% precision and offer the means to do much better. While WFC3 has helped open this new route, its full exploitation can come from a new technique, Parallel Astrometric Spatial Scanning (PASS), to measure parallax distances beyond a kiloparsec. I will review recent and expected progress.[ PDF slides ]
Komatsu, Eiichiro (MPA, Germany) [26 May, 15:00]
Angular diameter distances from strong lenses
Precise determinations of absolute distances such as the angular diameter distance as a function of redshifts play a crucial role in dark energy studies. There is so far only one known method to do this: Baryon Acoustic Oscillations (BAOs). Distant Type Ia supernovae give us only relative, rather than absolute, distances, as we do not know their absolute luminosities. In this talk, we present a new cosmic standard ruler: strong gravitational lensing. Roughly speaking, a measurement of the lensing time-delay of a strong lensing system tells us the physical size of the lens; thus, one can obtain the angular diameter distance to the lens by measuring angular positions of lensed images. Despite its promise, the previous studies focused only on either the time-delay or the image positions. A big advantage of this new method is that the effect of a uniform mass-sheet (i.e., external convergence) cancels out. However, a preliminary application of this method to B1608+656 and RXJ1131-1231 indicates that the inferred angular diameter distances to these systems are not as precise as one would naively guess given the precision of measurements. Our study shows that the current error budget is dominated by the uncertainties in the velocity dispersion and velocity anisotropy. The velocity anisotropy uncertainty can be reduced significantly by using the so-called “sweet-spot radius,” within which the mass of the lens galaxy can be determined nearly independently of the velocity anisotropy. The success of this method has a potential for a breakthrough in dark energy studies, as the resources one needs per distance are significantly less than those required for BAO surveys. [ PDF slides ]
Bono, Giuseppe (Univ. Roma II, Italy) [27 May, 11:00]
Cepheids and RR Lyrae as distance indicators and stellar tracers
We briefly introduce classical Cepheids as distance indicators. In particular, we focus our attention on optical and near-infrared Period--Wesenheit relations of Magellanic Cepheids. We also discuss the use of Galactic Cepheids to trace the abundance gradients across the thin disk. We also plan to introduce recent findings concerning optical, NIR and MIR Period-Luminosity and Period-Wesenheit relations of RR Lyrae stars and their impact on the cosmic distance scale. Moreover, we will outline the role that a homogeneous scale for cluster RR Lyrae has on the absolute age of Galactic globular clusters. [ PDF slides ]
Kudritzki, Rolf (Univ. Hawaii at Manoa, USA) [27 May, 15:00]
Supergiant stars and the Extragalactic Distance Scale
The ambitious goal to determine the Hubble constant with an accuracy of a few percent requires the development of alternative new methods which in comparison with the well established methods allow for independent assessments of possible systematic uncertainties. Low resolution multi-object spectroscopy of blue supergiant stars (BSGs) in spiral and irregular galaxies provides such an alternative. BSGs are the brightest stars in the universe at visual light with absolute magnitudes up to M_V = -10 mag. They are ideal stellar objects for the determination of extragalactic distances, in particular, because the perennial uncertainties troubling most of the other stellar distance indicators, interstellar extinction and metallicity, do not affect them. The quantitative spectral analysis of individual BSGs in galaxies provides stellar parameters and stellar metallicity, which are used to determine reddening and extinction from broad band photometry of each individual object. Accurate distances can then be determined from stellar gravities and effective temperatures using the "Flux Weighted Gravity - Luminosity Relationship (FGLR)". The determination of BSG stellar metallicities is a much more accurate constraint on the metallicity of the young stellar population in galaxies than the commonly used spectroscopy of the strong emission lines of HII-regions which are plagued by systematic uncertainties not well understood. This is important for accurate Cepheid distances and potential corrections of the period-luminosity relationship as a function of metallicity.
The BSG method will be introduced and the results accomplished so far in galaxy studies out to 8 Mpc will be presented together with a critical discussion of the strength and weaknesses of the method and its future perspectives in the era of TMT/E-ELT and JWST. [ PDF slides ]
Humphreys, Liz (ESO, Germany) [28 May, 11:00]
Megamaser Measurements of Extragalactic Distances and the Hubble Constant
Water megamasers at 22 GHz can enable mapping of AGN circumnuclear disks within 1 parsec of supermassive black holes. In combination with either acceleration or proper motion measurements of the masers, purely geometric distances can be obtained. In this talk, I will describe ways in which maser distances are being used to determine the Hubble constant with the aim of high-accuracy (3% uncertainty or better). The first method involves measuring the distance to nearby galaxy NGC 4258, and using it as an anchor to calibrate the standard candle distance scale. The second method involves using maser galaxies in the Hubble Flow to go directly to the Hubble constant. I will discuss the current status of results from both of these approaches and future prospects. [ PDF slides ]
Jha, Saurabh (Rutgers Univ., USA) [28 May, 15:00]
Surveying the Universe with Type Ia Supernovae
Type Ia supernovae (SN Ia) are exquisite tools with which to measure cosmological distances. They play a starring role in attempts to measure the scale and age of the Universe, to trace its expansion history, and to understand the dark energy that drives its current acceleration. I will describe how we use SN Ia, near and far, to address these questions, with a particular emphasis on the factors limiting the distance precision and accuracy (and thus, our cosmological inferences) from SN Ia. I will describe some contexts in which SN Ia distances are still limited by statistical uncertainties, but with the advent of large supernova surveys, systematic uncertainties are now largely dominant, and new approaches and new understanding are needed to deal with them. Major astrophysical systematics arise from SN Ia colors/reddening, progenitors, and environments. Finally, I will also discuss new applications of precise distances from SN Ia in current and upcoming surveys. [ PDF slides ]
Suyu, Sherry (Academia Sinica, Taiwan) [29 May, 11:00]
Time-delay Distances from Gravitational Lensing: Past, Present and Future
Strong gravitational lens systems with measured time delays between the multiple images can be used to determine the "time-delay distance" to the lens, which is primarily sensitive to the Hubble constant. I will describe the ingredients and newly developed techniques for measuring accurately time-delay distances with a realistic account of systematic uncertainties. A program initiated to measure the Hubble constant to <4% in precision from gravitational lens time delays is in progress, and I will present the first results and their implications. I will show the bright prospects of gravitational lens time delays as an independent and competitive cosmological probe.
[ PDF slides ]
Bonanos, Alceste (NOA, Greece) [29 May, 15:00]
Distances to early-type eclipsing binaries in the Local Group
Eclipsing binaries provide a direct, independent method for calibrating the extragalactic distance scale and thus determining the Hubble constant to high precision. I will review the method, its strengths and weaknesses, and the distances obtained to early-type eclipsing binaries in galaxies of the Local Group. [ PDF slides ]
Tully, Brent (Univ. Hawaii at Manoa, USA) [30 May, 11:00]
Cosmicflows-2 is a compendium of over 8000 distances measured primarily with 8 methods. There is sufficient interleaving between the methods to assure that they are on a common scale. Supernova Ia are among the methods and are given a robust zero point calibration. We determine a value of H0=75 from SNIa at 0.03<z<0.5.
The use of the spiral luminosity-linewidth correlation now involves mid-infrared photometry with Spitzer and WISE telescopes in space. All-sky uniformity is assured and reddening ceases to be an issue. We still find H0=75 km/s/Mpc.
Studies of peculiar velocity fields provide a strong constraint on H0 from an evaluation of any monopole term. A value of H0 too high for the distance measures causes infall and a value too low causes outflow. Modulo zero point issues, the value of H0 is constrained within a window of ±1.5 units by minimization of the monopole term.
[ PDF slides ]
Salaris, Maurizio (LJMU, UK) [30 May, 15:00]
Low-mass Post-main sequence standard candles
This talk will review the theoretical background of tip of the red giant branch, horizontal branch (non variable), red clump and asymptotic giant branch clump stars as distance indicators for the local universe. Particular attention will be paid to the most recent theoretical calibrations and comparisons with empirical constraints. [ PDF slides ]
Seitz, Stella (Munich Obs., Germany) [02 Jun, 11:00]
M31 distance indicators from PanSTARRS
PAndromeda is the 3 year M31-monitoring compaign of PanSTARRS-1. The Key-Project runs its own pipeline for the photometric alignment of the PS1-preprocessed data and applies rigorous masking of artefacts. Therefore our difference imaging light curves have well controlled photometric errors, and are suitable to identify and analyze short term events (novae and microlensing events) and to systematically study the variable star content of M31. To further characterise the PS1 sources we obtain HST-PHAT and IRAC photometry (with DOLPHOT/DAOPHOT) at the positions of PS1 resolved and variable sources and make use of public photometric catalogues like 2MASS. So far we have extracted and characterized ~2000 Cepheids in the M31 disk and halo (Kodric et al. 2013), ~300 eclipsing binaries and about ~4000 long periodic variables (LPVs).
We present Cepheid Period-Luminosity relations (PLR) in the infrared HST-PHAT bands (Kodric et al. 2014). We pay special attention to the dependency of the Cepheid PLR on the internal scatter and clipping procedure as discussed by Efsthathiou (2014). We compare our results to Riess et al. (2012) obtained for a smaller Cepheid sample. The evidence for a broken slope of the PLR at log P[d]~1 is investigated. The still to come final analysis of the full 3yr data will yield more long periodic Cepheids and hence allow to analyse the slope of the PLR up to log P[d]~2.
The LPVs period luminosity relation is studied in the Infrared using IRAC photometry. The status of the eclipsing binary analysis will be summarized in the talk of C.-H. Lee. The KP's own PS1 data products (and linked HST-PHAT photometry) can be made available for external collaborators. [ PDF slides ]
Cantiello, Michele (Teramo Obs., Italy) [02 Jun, 15:00]
The Surface Brightness Fluctuations method: Bridging the gap between the Local Group and cosmological distances
The SBF method was introduced in the late 1980's as a viable distance indicator for elliptical galaxies up to 20 Mpc. After more than two decades since its first application, a deeper understanding of the astrophysical processes that generate the SBF signal and the improved characteristics of observing facilities allowed to significantly extend the range of use, and the class of useful targets of the technique. To date, in fact, SBF are measured for distances ranging from within the Local Group out to ~150 Mpc, and for galaxies spanning a wide range of morphologies and masses. In my presentation I will:
- give a general introduction to the method, describing how it works, and why;
- present the main observational and "theoretical" results obtained with SBF in the last ~20 years;
- discuss the perspectives of the method with the advent of Gaia, JWST and future class of ground-based large telescopes. [ PDF slides ]
Fiorentino, Giuliana (Bologna Obs., Italy) [03 Jun, 11:00]
Crossing the Instability Strip: from super-giants to dwarfs
During their evolutionary life some stars cross the Instability Strip and start to pulsate. Depending on their mass and luminosity they show different pulsation properties thus tracing their evolutionary state and providing sounds constraints on the star formation history of the host stellar system. More importantly, they show periods very well connected to the instrinsic stellar parameters such as luminosity and/or colour, this allows us to use them as distance indicators.
I will review some distance indicators that have (or will have) a key role in the extragalactic distance scale within a very large mass range: Ultra Long Period Cepheids (M>10-12Msun), Classical Cepheids (3Msun<M<10-12Msun) and SX Phoenicis stars (M<1.5Msun), highlighting the problems connected with their use as standard candles. [ PDF slides ]
Anderson, Richard (Geneva Obs., Switzerland) [03 Jun, 15:00]
New Challenges for Cepheid-based Distances
Classical Cepheids are among the most precise standard candles and, in conjunction with type Ia supernovae, have enabled a calibration of the Hubble constant that is precise to about 3%. However, tension between different calibrations of the Hubble constant suggests that systematic effects may be biasing our cosmic yardsticks.
Approaching the subject from a stellar astrophysics perspective, I present theoretical and observational investigations of systematic effects that may present challenges for the calibration of the Cepheid period-luminosity relation. Part one presents the first detailed (theoretical) investigation of the effect of rotation on populations of classical Cepheids. The observational second part then presents recently discovered modulation in the radial velocity variability of Cepheids and considers the importance of modulation for Baade-Wesselink-type distances.
Further work in progress is discussed, concentrating on ways of exploiting these new findings and mitigating the systematics they may introduce to further improve the accuracy of Cepheid-based distances. [ PDF slides ]
Stanek, Kris (Ohio State Univ., USA) [04 Jun, 11:00]
Still Undermining the Public Confidence in Cosmological Distance Ladder
While the cosmological distance ladder is significantly sturdier now that it was 20 years ago, a number of major issues remain, and I will discuss in some detail two most important of them: blending of Cepheids and metallicity dependence of Cepheid PL relation.
Unfettered by my own negativity, I will then discuss an ongoing effort at OSU to measure distances to nearby glaxies using LBT light curves combined with HST photometry.[ PDF slides ]
Wong, Kenneth (Academia Sinica, Taiwan) [04 Jun, 15:00]
The Effect of Environment on H0 from Gravitational Lens Time Delays
We present a new lensing framework for treating line-of-sight (LOS) galaxies. We test our framework using a set of simulations using a single perturber to study where the shear approximation is not valid and where non-linear effects are important. We find that our LOS framework can reproduce the fitted lens properties of realistic fields without bias and scatter that is smaller than typical measurement uncertainties. Models with an external shear or models that ignore the environment both have larger scatter in the recovered parameters of the fit and a bias of ~10% in the inferred Einstein radius of the main lens galaxy. This bias is due to the convergence of perturbing galaxies; the external convergence can be included but must be done explicitly in shear models. In our approach the convergence and shear arise self-consistently from an underlying mass distribution.
We generate mock time delay lenses and place them in realistic lines of sight generated from photometric and spectroscopic data in fields containing known lens systems to determine how perturbations from the external lens environment (including mass in the foreground, background, and at the lens redshift) affect physical parameters derived from lens models, such as the lens galaxy Einstein radius, mass profile slope, ellipticity, and orientation, as well as the Hubble Constant (H0). We quantify how uncertainties in both characterization of the lens environment and in measured lens model constraints affect the recovered parameters. The environment generally contributes larger scatter to the derived Einstein radius, mass profile slope, and orientation of the lens galaxy, and sometimes contributes larger scatter in H0 and lens galaxy ellipticity. We isolate individual sources of uncertainty in the characterization of the lens environment and find that for galaxy-scale perturbers, scatter in the galaxy mass is the dominant effect. We compare the distribution of H0 values determined by simple shear models to the distribution recovered by our environment treatment. The simple shear models show a residual bias and large scatter, even when corrected with a 1-kappa_eff term, compared to our full environment models that have ~1% bias. We investigate how well an ensemble of new time delay lenses from LSST data will be able to recover H0 given assumptions about how well LSST will be able to reconstruct the mass distribution along the line of sight. For an ensemble of 500 four-image time delay lenses from LSST, the statistical error on H0 due to environment effects will be small (~0.3%), but there is a residual bias of ~2%. [ PDF slides ]
Inno, Laura (ESO, Germany) [05 Jun, 11:00]
The 3D Structure of the Magellanic Clouds Traced by Classical Cepheids
Classical Cepheids play a key role in constraining the cosmic distance scale. They are the most popular primary distance indicators and obey well-defined Period-Luminosity (PL) and Period-Wesenheit (PW) relations. In particular, the PW relations are reddening independent and minimally affected by metallicity. Moreover, PW relations based on optical and near-infrared bands (NIR) are linear over the entire period range with a very low dispersion, and they can be safely adopted to derive Cepheid relative distances with high precision. We have recently developed new light curve templates to estimate the mean magnitude from single epoch measurements in the NIR bands. The new templates have been constructed on the basis of well-sampled optical and NIR light curves that we collected for more then 500 calibrating Galactic and Magellanic Cepheids. By applying the template to the IRFS/SIRIUS single epoch measurements for more than 7000 Cepheids in the MCs, we estimated their relative distances with an accuracy better than one percent.
We found that the LMC has a complex vertical structure along the line of sight, with evidence of a non-planar matter distribution. The SMC is more homogeneous, its thickness increases along the line-of-sight and the increase in the spread appears to be connected with the LMC. To constrain the kinematics and the metallicity distribution of the young populations we already collected with VIMOS at VLT low-resolution spectra for more than 900 Cepheids (~300 LMC and ~600 SMC). We plan to present preliminary results concerning the radial velocities. [PDF slides]
Dall'Ora, Massimo (INAF-OACN, Italy) [05 Jun, 11:15]
Matching different distance indicators: the case of M95 and the use of the Type IIP SNe as standardized candles.
Extragalactic distance scale relies basically on the Cepheids. However, no general consensus have been reached on both the slope and the zero point of their Period-Luminosity relations, which may differ from galaxy to galaxy. It is therefore interesting to found systems for which it is possible to estimate the distance by using independent indicators, possibly belonging to different stellar populations and/or systemic properties. One of them is the spiral galaxy NGC 3351 (M95), in the Leo's group, whose distance has been estimated by using several techniques, including Cepheids, the Tip of the Red Giant Branch, the Planetary Nebulae Luminosity Function, and the Tully-Fisher relation. Moreover, the Type II Plateau (IIP) supernova SN 2012aw exploded in M95, providing us the possibility to use it as standardized candle and to compare the distance obtained with this method with those obtained with the other available indicators. We will also briefly discuss the potential of the Type IIP SNe distance calibration to bridge the Cepheids and the SNe Ia distance scale. [ PDF slides ]
Pietrzynski, Grzegorz (Warsaw Obs., Poland) [05 Jun, 15:00]
The Araucaria project: Precise and accurate calibration of the cosmic distance scale based on observations of eclipsing binaries.
We will present recent results on the distance determination to the LMC and SMC based on very rare late-type long-period eclipsing binaries. It has been demonstrated that using accurate photometric and spectroscopic data and the well-established surface-brightness color relation, one can measure distances to individual systems with an accuracy of about 3 %. With the discovery of a few dozen such systems in the Magellanic Clouds, we are in a position to be able to measure distances to the LMC and SMC with 1 and 2 % accuracy, respectively. [ PDF slides ]
Casertano, Stefano (STScI, USA) [06 Jun, 11:00]
High precision parallax measurements with HST - the distances to Galactic Cepheids and the Hubble Constant
A recently implemented observing technique for the Wide Field Camera 3 on HST is capable of yielding astrometric measurements with a precision of about 20 µas, an order of magnitude better than could previously be achieved with HST. Preliminary results from a project to measure trigonometric parallaxes of long-period Galactic Cepheids demonstrate the potential precision of this method, but also underscore the need for more careful calibration of various instrumental effects that become relevant below 100 µas. When complete in early 2015, our program will obtain distance measurements for 19 long-period Galactic Cepheids, with typical errors of a few percent per target at distances of 1 to 3 kpc. These Cepheids will form the best available calibrator for the local value of the Hubble Constant (expected error 1-2%) until the completion of the Gaia mission. [ PDF slides ]
Hoffmann, Samantha (Texas A&M Univ. Univ, USA) [06 Jun, 15:00]
MEGA-SH0ES: Searching for Cepheid Variables in Type Ia Supernova Host Galaxies
The MEGA-SH0ES project aims to measure the Hubble constant to percent-level uncertainty. As part of this ongoing effort, we determine accurate and precise Cepheid distances to host galaxies of type Ia supernovae within 50 Mpc.
I will present preliminary results from our latest HST/WFC3 observations, in which time-series data is obtained using a long pass filter (F350LP) to detect variability while conserving orbits and infrared images (F160W) are used to construct a precise P-L relation with low systematic uncertainty. We will combine the new targets with the ones previously analyzed in Riess et al. (2011) and calibrate the Extragalactic Distance Scale with a record 17 SNeIa host galaxies. [ PDF slides ]
Schmidt, Brian (ANU, Australia) [09 Jun, 11:00]
SkyMapper and the Extragalactic Distance Scale
Measuring the Extragalactic Distance Scale has become precision science. The SkyMapper Telescope seeks to provide precise calibration for stars, galaxies, and transient objects across the southern sky through several surveys. I will discuss the Southern Sky Survey and how it links into the commmunity's efforts to measure the Hubble Constant and the distance-redshift relation with ever-increasing precision. [ PDF slides]
Gieren, Wolfgang (Univ Concepción, Chile) [09 Jun, 15:00]
The Araucaria Project: Improving classical Cepheids as standard candles
The Araucaria method of deriving distances to nearby galaxies with samples of classical Cepheids is presented. The effect of systematic uncertainties on the derived distance moduli (reddening, reddening law, metallicity, crowding/blending, circumstellar envelopes, nonlinearity of PL relations) is discussed. The advantages and disadvantages of Cepheid distance work in mid-infrared passbands, as compared to the near-infrared, are briefly discussed.
Finally, work of our group on classical Cepheids in LMC eclipsing binaries, and its potential for a more detailed understanding of the physical properties of these standard candles is reviewed. [ PDF slides ]
Coppola, Geppina (Capodimonte Obs., Italy) [10 Jun, 11:00]
New theoretical Period-Luminosity-Metallicity and Period-Wesenheit-Metallicity relations for RR Lyrae stars
We present new predicted Period-Luminosity-Metallicity (PLZ) and Period-Wesenheit-Metalliticity (PWZ) relations for RR Lyrae stars. Current findings are based on a detailed set of nonlinear, time-dependent convective hydrodynamical models of RR Lyrae. To properly trace the metallicity dependence we adopted seven chemical compositions covering the typical range of iron abundances of both cluster and field RR Lyrae stars. The pulsation models, at fixed metal content, cover a broad range in effective temperature while the mass and the luminosity were fixed according to horizontal branch evolutionary models. We constructed pulsation models for fundamental and first overtone pulsators and they were integrated in time until they approach the limit cycle stability. Theoretical predictions (magnitude, colors) were transformed into the observational plane by adopting static atmosphere models. We also discuss new optical and NIR PLZ and PWZ relations together with the new instability strips. Finally, we use the new theoretical framework to estimate the distance to the Carina dSph by using optical PWZ relations of RR Lyrae stars and to constrain their pulsation properties. [ PDF slides ]
Kanbur, Shashi (SUNY-Oswego, USA) [10 Jun, 15:00]
Using the Structural Properties of Cepheid/RR Lyrae Light Curves in Distance/Metallicity Estimation
The Structural Porperties of Cepheid/RR Lyrae light curves theoretically convey important information about the global properties of these stars such as mass, luminosity, effective temperature and metallicity. For Cepheids, the Cepheid PL relation is really a projection of the Cepheid PLC relation. One possible way to improve the Cepheid PL relation is to search for a light curve structure parameter that is a proxy for the color term in a PLC relation. Possible advantages include reduced dispersion and insensitivity to reddening corrections. Possible disadvantages include the requirement of more accurate light curves.
Here we review some possibilities for such a PL-light curve structure relation using Principal Component Analaysis and Fourier decomposition. We review preliminary results using OGLE Magellanic Cloud data that shows a significant improvement when using a third light curve parameter in a PLC relation. A similar approach has beed used for RR Lyraes. We review these efforts and some recent results connecting RR Lyrae light curve structure and metallicity. [ PDF slides ]
Hosek, Matthew (Univ. Hawaii at Manoa, USA) [11 Jun, 11:00]
An FGLR Distance to Metal-Poor Dwarf Galaxy NGC 3109
I will present a quantitative analysis of the low-resolution (~4.5Å) spectra of 12 late-B and early-A blue supergiants (BSGs) in the metal-poor dwarf galaxy NGC 3109. We use a modified method of analysis which does not require use of the Balmer jump as an independent Teff indicator, as used in previous studies. We determine stellar effective temperatures, gravities, metallicities, reddening, and luminosities, and combine our sample with the early-B type BSGs analyzed by Evans et al. (2007) to derive the distance to NGC 3109 using the flux-weighted gravity–luminosity relation (FGLR). We find a distance modulus of 25.55±0.09 (1.27 Mpc) that compares well with Cepheid and Tip of the Red Giant Branch distances. In addition, we derive an average Fe-group metallicity of [Z] = -0.67±0.13, higher than the oxygen abundance of [Z] = -0.93 ±0.07 found by Evans et al. (2007), suggesting a low alpha/Fe ratio for the galaxy. The agreement between the FGLR and Cepheid distances indicates that metallicity does not have a significant effect on the Cepheid Period-Luminosity Relation between [Z] = -0.3 and [Z] = -0.7, consistent with the findings of the Araucaria Project. The FGLR itself is very consistent with those found in other galaxies, demonstrating the reliability of the FGLR as a measure of extragalactic distances. [ PDF slides ]
Braga, Vittorio (Univ Roma-II, Italy) [11 Jun, 11:45]
Distance determination to M4 with optical, NIR and MIR photometry of RR Lyrae
We give a distance determination to M4, the nearest among globular clusters. Accurate optical, NIR and MIR photometry provided us periods and mean magnitudes of RR Lyrae stars that we used to determine Period-Luminosity (PL) and Period-Wesenheit relations to which these variables obey. By calibrating the observed optical-NIR relations with theoretical Period-Luminosity-Metallicity (PLZ) and Period-Wesenheit-Metallicity (PWZ) relations derived from models, we obtain a distance modulus to M4 equal to 11.296±0.003±0.026 mag from PLZ and 11.267±0.011±0.035 mag from PWZ. MIR PL relations were calibrated using WISE data of four Galactic RR Lyrae. We obtain distance moduli of 11.58±0.10 mag and 11.53±0.11 mag at 3.6 and 4.5µm, respectively. We plan to derive IRAC PL relations to improve our estimates from MIR bands.
Distance moduli from optical-NIR PLZ and PWZ relations agree quite well with distance module determinations to M4 found in the literature and obtained with other methods such as 11.18±0.18 mag from the study of the radial velocity and proper motion dispersion (Peterson et al. 1995); 11.19±0.01 mag from the use of the surface-brightness technique -a variant of the Baade-Wesselink method- applied to RR Lyrae (Liu & Janes 1990) and 11.30±0.05 mag from a very accurate estimate from detached eclipsing binaries (Kaluzny et al. 2013). [ PDF slides ]
Arnaboldi, Magda (ESO, Germany) [11 Jun, 15:00]
Parent stellar populations and planetary nebulae: population effects on the luminosity function, PN specific frequencies and PN expansion velocities
Extended, deep narrow band imaging surveys and their spectroscopic follow-up are now available for the study of PN populations in the brightest cluster galaxies in the nearby clusters. These samples are now deep enough to cover similar magnitudes intervals from the PNLF brightest cut-off as for PN population in the LMC, M31 and other local group galaxies. Hence it has become possible to investigate population effects on the 2.5 mag of the PNLF. We discuss which physical mechanism may alter the evolution of a planetary nebulae envelope and its central star in the halo of BCGs with respect to star forming and disk galaxies. [ PDF slides ]
Mould, Jeremy (Swinburne, Australia) [12 Jun, 11:00]
The local velocity field
Knowing the local velocity field is vital to determining the Hubble Constant at zero redshift. To illustrate, peculiar velocities can be as large as 20% at Virgo and 10% at Coma. However, knowledge of the density field can vastly reduce this concern, as peculiar velocities are the divergence of the density field and can be calculated. Current models are presented. I also discuss the state of the art of extragalactic distance indicators, including Baryon Acoustic Oscillations, the SNIa standard candle, the Fundamental plane (FP) for early type galaxies and the Tully Fisher relation (TFR). When Tully, Fisher, Faber & Jackson were young, galaxy scaling relations were popular distance indicators. They were replaced by supernovae, which are much more accurate. However, in the case of clusters of galaxies, statistics can come to our help with n0.5 and render the TFR and the FP competitive as few-percent distance measurements. The 6dFGS and TAIPAN use large samples to take advantage of this. A TFR is presented for SAMI pilot galaxies, including a 3D TFR for galaxies with bulges. In addition, H-alpha profiles from SAMI red datacubes are shown. Only a fraction of the targets are detections, however. The TFR has long been known to arise from dynamical equilibrium in disk galaxies and “the halo disk conspiracy.” The FP, on the other hand, arises from serial galaxy accretion which can be parameterized as a simple differential growth equation in dlog m / dlog sigma with dissipation and mass loss terms. The symbols here refer to galaxy mass, m, and velocity dispersion, sigma. TAIPAN and 6dFGS are Australian Astronomical Observatory redshift surveys. The SAMI Galaxy Survey is based on observations made at the Anglo-Australian Telescope. The Sydney- AAO Multi- object Integral field spectrograph (SAMI) was developed jointly by the University of Sydney and the Australian Astronomical Observatory. CAASTRO is the Centre of Excellence for All Sky Astrophysics. [ PDF slides ]
Leibundgut, Bruno (ESO, Germany) [12 Jun, 15:00]
The IR behaviour of SNe Ia
The infrared light curves of type Ia supernovae have been suggested as excellent distance indicators. The decreased dependence on absorption corrections, which by now have become a notorious feature of supernova cosmology, and the apparently uniform behaviour of SNe Ia in the near-infrared are the main reasons for this new approach. Several ongoing and future observing programmes are targeting this wavelength range.
We have assembled the available IR data of SNe Ia for a detailed study of the light curves. Most SN Ia IR light curves are displaying a distinctive form with two maxima separated by about 3 to 4 weeks. The uniformity at first maximum for SNe Ia is confirmed. There indeed is an impressively low scatter in the IR luminosity at peak. Thereafter the light curves start to display a very varied behaviour and the second maximum shows clear correlations hinting at differences in the amount of nickel in the explosions. The IR light curves hold clues to the nature of the thermonuclear explosions, which should help in further refining SNe Ia as cosmological tools. [ PDF slides ]
Urbaneja, Miguel (Univ. Innsbruck, Austria) [13 Jun, 11:00]
Calibrating the FGLR with LMC supergiant stars
We present in this talk our on-going efforts on calibrating the Flux-weighted Gravity-Luminosity relationship of Blue Supergiant stars with a detailed study of stars in the Large Magellanic Cloud. Particular emphasis will be given to discuss potential sources of uncertainties due to differences in the techniques employed in nearby and distant galaxies. [ PDF slides ]
Sanchez, Ariel (MPE, Germany) [13 Jun, 15:00]
Baryon Acoustic Oscillations
The signature of baryon acoustic oscillations (BAO) imprinted in the clustering of galaxies offers a robust standard ruler that can be used to measure the cosmological distance-redshift relation, probing in this way the expansion history of the Universe. Driven by the potential of BAO observations to shed light on the physics behind the accelerated expansion of the Universe, several groundbreaking galaxy surveys are currently underway. These surveys will measure the LSS of the Universe with unprecedented precision, providing new insights not only on the origin of cosmic acceleration, but also on many other important physical parameters. The ongoing Baryon Oscillation Spectroscopic Survey (BOSS) is an example of these new surveys. In this talk I review our theoretical understanding of the BAO signal and the details of the analysis of these measurements. I also describe the cosmological implications of the latest BAO measurements in BOSS, with an emphasis on the problem of understanding cosmic acceleration. [ PDF slides ]
Mendez, Roberto (Univ. Hawaii at Manoa, USA) [16 Jun, 11:00]
I will start with a short historical introduction; the younger generations may ignore that PNLF was among the first methods that pointed to H0~70. I will explain how the method works, present a few new PNLF distances, and explain in particular how the empirical success of the method presents a challenge to our current picture of the transition from AGB stars to white dwarfs. I will also describe numerical simulations of the PNLF, their limitations, and what we would need to make better ones. [ PDF slides ]
Agnello, Adriano (UCSB, USA) [16 Jun, 15:00]
The next decade of time-delay distances
Cosmographic inference from time-delay lenses is complementary to high-redshift probes, such as CMB experiments, which cannot measure the Hubble constant directly. Current analyses of time-delay lenses have yielded new results on the Hubble constant, curvature and dark energy equation of state. At present, a sammple of five time-delay lenses are being analysed (aiming at 4% precision and accuracy on H0). I will outline the roadmap towards a measurement of H0 with 1% uncertainty (statistical and systematic). A robust characterization of (possible) hidden systematics will be possible by examining a sample of nine time-delay lenses, with a variety of ancillary data which I will describe. This will act as a pathfinder in view of upcoming large samples of lensed quasars, where the uncertainties will come essentially from systematics. Our searches into the Dark Energy Survey are expected to unveil ~1200 new lensed quasars (~0.2 per square degree) upon completion. I will describe how the search for lensed quasars is structured, the modelling challenges for this new large sample of objects and how our collaboration is currently assessing all the known sources of systematic uncertainties. [ PDF slides ]
Longobardi, Alessia (MPE, Germany) [17 Jun, 11:00]
The PNLF of the halo and IC population in M87
Utilising photometric observations obtained with Subaru-CAM, we acquired a sample of Planetary Nebulae (PNe) to investigate the diffuse light in the outer regions of the elliptical galaxy M87. We extracted a complete imaging catalogue of ~700 emission objects down to m5007=28.4 and out to a radial distance of 150 kpc, making this PN sample one of the largest both in number of tracers and in radial extent. The resulting PNe sample shows the superposition of two stellar populations, both a halo and intra-cluster light component (ICL). The ICL component is found to contribute three times more PNe than the bound halo population.
The imaging survey was followed by a spectroscopic follow-up (FLAMES/GIRAFFE) that lead to a sample of hundreds spectroscopically confirmed PNe. This PNe have m5007 magnitudes from the bright cut-off, to 2.5 mag down the LF and same radial extent than the photometric objects. With these results we are able to question the shape of the PNLF for both the halo and ICL PNe making use of an unprecedented number of spectroscopically confirmed objects. Moreover we are able to quantify the contribution of contaminants, such as Ly-alpha and OII emitters, to the observed PNLF. [ PDF slides ]
Yuan, Wenlong (Texas A&M Univ., USA) [17 Jun, 11:45]
The Cepheid P-L relation at near infrared wavelengths: M101 and the Milky Way
As part of an effort to further reduce the uncertainty in the Hubble constant to the percent level, we measured the distance to M101 (host of type Ia SN 2011fe) using the Cepheid P-L relation at near-infrared wavelengths. We performed PSF photometry on two fields in this galaxy, which were observed with HST ACS and WFC3 at V, I and H. Over 800 Cepheids were used to fit the optical P-L relations and a subset of these were recovered in the H-band images. Preliminary results will be presented during the talk.
We will also introduce our ongoing project in support of parallax observations of nearby (D < 4 kpc), long-period (P>10d) fundamental-mode Cepheids using a novel technique with HST. The parallax method provides a direct calibration of the Galactic Cepheid P-L relation that is free of assumptions. We are using the CTIO 1.3-m telescope to obtain sparsely-sampled H-band light curves and provide phase corrections for the ongoing HST observations. [ PDF slides ]
Groenewegen, Martin (OMA, Belgium) [17 Jun, 15:00]
Understanding the Baade-Wesslink based distance scale for Cepheids
If other distances are not available, such as parallax measurements or main-sequence fitting of clusters, the Baade-Wesselink method is a good alternative to get the distance to a Cepheid. Required are a lightcurve in 2 bands (typically V and K), and the radial velocity curve. The variation in colour is transformed in to a variation in angular diameter via a surface brightness relation, the RV curve is integrated to get the absolute variation. The ratio of the two gives the distance.
There are issues however... There is the p-factor that transforms the radial velocity into pulsational velocity. Also, two groups (my work, and that of Jesper Storm) find different results on what seemingly is identical data using the same basic method. During my stay I hope to investigate the cause of these differences.[ PDF slides ]
Storm, Jesper (AIP, Germany) [18 Jun, 11:00]
Constraining the metallicity effect on the Cepheid Period-Luminosity relation using the near-IR surface brightness method
The effect of metallicity on the Cepheid Period-Luminosity relation is of fundamental importance for the calibration of the extra-galactic distance. The effect on both the slope and the zero point of the relation has been determined from different methods but the results have covered quite a large range and even the sign of the effect on the Period-relation zero point has been in doubt. We have studied the effect using the near-IR surface brightness method which gives direct distances to individual Cepheids. To get good leverage on the range of metallicities we have studied a large (70 stars) sample of galactic Cepheids and compared it to a significant (36 stars) sample of LMC Cepheids and a few (5) SMC Cepheids. We find that in the K-band, which is the most relevant for extra-galactic work as it is only weakly dependent on reddening, the metallicity effect is small and within the errors not distinguishable from zero.
I will describe how we have overcome the problem that the method gave rise to a different slope of the Period-Luminosity relation for galactic and LMC Cepheids by using an empirical correction to the projection factor converting the observed radial velocities into the pulsational velocities required for the analysis. This issue still lacks a proper physical explanation and I will discuss some of the work which we have undertaken to get a proper physical understanding of the problem.
I will finally describe the continuation of this work which includes new data for a significantly increased sample of SMC stars (for a total of more than 30 Cepheids) and an expanded sample of galactic Cepheids. [ PDF slides ]
Lee, Chien-Hsiu (MPE, Germany) [18 Jun, 15:00]
Andromeda as Distance Anchor
Distance anchors are corner stones of extragalactic distance scale. In this talk we will present our survey for eclipsing binaries in the nearest spiral galaxy, Andromeda, using the Pan-STARRS data (PAndromeda). We have detected ~300 eclipsing binaries towards Andromeda, where several of them are brighter than 20 mag in V, render spectroscopic follow-up and make an accurate distance estimate feasible. [ PDF slides ]
Taubenberger, Stefan (MPA, Germany) [19 Jun, 11:00]
Distance measurements with Type IIP supernovae
When it comes to measuring cosmic distances, core-collapse supernovae (SNe) of type IIP have - at least over the past 20 years - lived in the shadow of their more luminous and more homogeneous siblings, the thermonuclear SNe of type Ia. However, while type Ia SNe are splendid relative distance indicators, type IIP SNe are arguably better suited to measure absolute distances, avoiding the propagation and accumulation of calibration errors through the consecutive steps of the cosmic distance ladder.
In this talk, I will give a brief review of previous attempts to measure distances with type IIP SNe, either by treating them as standardisable candles, or by applying the expanding-photosphere method (EPM), which relies on a blackbody approximation, justified by the dominance of continuum processes in the spectrum formation of type IIP SNe. Modern variants (SEAM) that make use of detailed spectral modelling to overcome shortcomings of the classical EPM are also presented. I will then concentrate on a particular SEAM implementation based on the radiative-transfer code TARDIS, which we are currently developing. With this method, distance measurements shall be obtained for a dedicated sample of type IIP SNe, observed at the 2.2m UH88 Telescope in the case of nearby events (0.01<z<0.04), or at the 10.4m GTC for more distant SNe (0.04<z<0.30).The observing strategy for these SNe has been taylored to allow for an optimum distance determination with SEAM.
Eventually, the precise absolute distances measured in this manner will be used for an independent determination of the Hubble constant, H0. [ PDF slides ]
Ngeow, Chow-Choong (NCU, Taiwan) [19 Jun, 15:00]
The use of ultra long period Cepheids in distance scale work
Ultra-long period Cepheid (ULPC) are classical Cepheids with periods longer than 80 days. It has been known for a long time that ULPCs appeared as outliers in the period-luminosity (PL) relations defined by the shorter period Cepheids, and hence they are ignored in usual distance scale applications. However, Bird et al (2009) suggested that ULPCs follow a different PL relation than their shorter period counterparts, at which their period-Wesenheit relation is almost flat with an absolute magnitude in Wesenheit function of ~ -9.5mag. This suggested that ULPC could be used to probe a further distance than the shorter period Cepheids. For example, it has been argued that ULPC can be used to find distances out to ~100Mpc with next generation extreme large telescopes, at which the galaxies are freed from Hubble flow, and hence obtaining the Hubble constant in "one-step".
In this talk, I will first give a brief overview of ULPC and their potential application in distance scale work. I will then present some of our recent effort to search for ULPC in M31 using the data from Palomar Transient Factory. I will also discuss our work on comparing their Fourier coefficients to those from Mira variables, at which the preliminary results suggested the Fourier coefficients for them are quite similar. This hints the possibility of mis-classification of ULPC as Mira variable stars, or vice versa, based on light curves alone. I will end the talk with some prospect of using ULPC in future distance scale determination. [ PDF slides ]
Ishida, Emille (MPA, Germany) [20 Jun, 11:00]
Challenges in SN photometric classification
The problem of supernova (SN) photometric identification will be extremely important for large surveys in the next decade. This might resemble a high-redshift issue at first glance, but any modern statistical algorithm aiming at photometricaly classifying the first generation of SNe from these new surveys will rely on low-redshift counterparts for training. In this context we have two major issues to deal with: how to improve the currently available photometric classification methods and how to build a consistent training set, formed from all the SNe we already observed up to now, which would allow us to make reliable classifications before the completion of a specific survey. Both issues will be addressed in this talk. [ PDF slides ]
Macri, Lucas (Texas A&M Univ., USA) [20 Jun, 15:00]
Absolute calibration of the near-infrared Leavitt Law in the Large Magellanic Cloud
I present results from the Large Magellanic Cloud Near-Infrared Synoptic Survey, which covered ~18 sq deg of the central region of this galaxy in J, H & Ks to a depth of Ks~17 mag and obtained an average of 16 epochs in each filter. Our catalog contains more than 5×106 sources, including over 1400 Cepheids discovered by the OGLE survey. Our LMC Cepheid sample represents a 15-fold increase in the number of these variables with time-resolved, multi-band near-infrared photometry. We combine our large Cepheid sample and a recent precise determination of the distance to the LMC to derive a robust absolute calibration of the near-infrared Period-Luminosity relations for fundamental-mode and first-overtone pulsators, with 2× better constraints on the slopes than previous work. [ PDF slides ]