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TOPIC: Determining Distance
Blobrana


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RE: Determining Distance
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Determining the distance to a galaxy:

z = (lambda - lambda_0)/lambda_0

z = Red shift

lambda = wavelength shift measured

lambda_0 = Wavelength 

Red shift = Recession velocity / Speed of light

Distance = Recession velocity / Hubble constant

Hubble constant = 71 km/s per megaparsec



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Blobrana


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Title: The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. III. NGC 4038/39 and NGC 5584
Author: In Sung Jang, Myung Gyoon Lee

We present the tip of the red giant branch (TRGB) distances to Type Ia supernova (SNe Ia) host galaxies NGC 4038/39 and NGC 5584. Based on the deep images constructed using archival Hubble Space Telescope data, we detect red giant branch stars in each galaxy. VI photometry of the resolved stars and corresponding I-band luminosity functions show the TRGB to be at I_{TRGB} = 27.67 ± 0.05 for NGC 4038/39 and I_{TRGB} = 27.77 ± 0.04 for NGC 5584. From these estimates, we determine the distance modulus to NGC 4038/39 to be (m-M)_0 = 31.67 ± 0.05 (random) ± 0.12 (systematic) (corresponding to a linear distance of 21.58 ± 0.50 ± 1.19 Mpc) and the distance modulus to NGC 5584 to be (m-M)_0 = 31.76 ± 0.04 (random) ± 0.12 (systematic) (corresponding to a linear distance of 22.49 ± 0.41 ± 1.24 Mpc). We derive a mean absolute maximum magnitude of SNe Ia of M_V = -19.29 ± 0.08 from the distance estimates of five SNe Ia (including two SNe in this study and three SNe Ia from our previous studies), and we derive a value of M_V = -19.19 ± 0.10 using three low-reddened SNe Ia among the five SNe Ia. With these estimates, we derive a value of the Hubble constant, H_0 = 69.8 ± 2.6 (random) ± 3.9 (systematic) km/s/Mpc and 72.2 ± 3.3 (random) ± 4.0 (systematic) km/s/Mpc, respectively. The value from the five SNe is similar to those from the cosmic microwave background analysis, and not much different within errors, from those of recent Cepheid calibrations of SNe Ia. The value from the three SNe is between the values from the two methods.

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Blobrana


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Title: A climb on the cosmic ladder with stellar twins
Author: P. Jofre, T. Maedler, G. Gilmore, A. Casey, C. Soubiran, C. Worley

Distances to stars are key to revealing a three-dimensional view of the Milky Way, yet their determination is a major challenge in astronomy. Whilst the brightest nearby stars benefit from direct parallax measurements, fainter stars are subject of indirect determinations with uncertainties exceeding 30%. We present an alternative approach to measuring distances using spectroscopically-identified twin stars. Given a star with known parallax, the distance to its twin is assumed to be directly related to the difference in their apparent magnitudes. We found 175 twin pairs from the ESO public HARPS archives and report excellent agreement with Hipparcos parallaxes within 7.5%. Most importantly, the accuracy of our results does not degrade with increasing stellar distance. With the ongoing collection of high-resolution stellar spectra, our method is well-suited to complement Gaia.

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Blobrana


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Tip of the Red Giant Branch
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Title: The Tip of the Red Giant Branch Distances to Type Ia Supernova Host Galaxies. II. M66 and M96 in the Leo I Group
Authors: Myung Gyoon Lee, In Sung Jang

M66 and M96 in the Leo I Group are nearby spiral galaxies hosting Type Ia Supernovae (SNe Ia). We estimate the distances to these galaxies from the luminosity of the tip of the red giant branch (TRGB). We obtain VI photometry of resolved stars in these galaxies from F555W and F814W images in the Hubble Space Telescope archive. From the luminosity function of these red giants we find the TRGB I-band magnitude to be I_{TRGB}=26.20±0.03 for M66 and 26.21±0.03 for M96. These values yield distance modulus (m-M)_0=30.12±0.03 (random)±0.12 (systematic) for M66 and (m-M)_0=30.15±0.03 (random)±0.12 (systematic) for M96. These results show that they are indeed the members of the same group. With these results we derive absolute maximum magnitudes of two SNe (SN 1989B in M66 and SN 1998bu in M96). V-band magnitudes of these SNe Ia are ~0.2 mag fainter than SN 2011fe in M101, the nearest recent SN Ia. We also derive near-infrared magnitudes for SN 1998bu. Optical magnitudes of three SNe Ia (SN 1989B, SN 1998bu, and SN 2011fe) based on TRGB analysis yield a Hubble constant, H_0=67.6±1.5 (random)± 3.7(systematic) \kmsMpc. This value is similar to the values derived from recent WMAP9 results, H_0=69.32±0.80 \kmsMpc. % and from Planck results, H_0=67.3±1.2 \kmsMpc, but smaller than other recent determinations based on Cepheid calibration for SNe Ia luminosity, H_0 = 74 ±3 km s^{-1} Mpc^{-1}.

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Blobrana


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Measuring the Universe More Accurately Than Ever Before

After nearly a decade of careful observations an international team of astronomers has measured the distance to our neighbouring galaxy, the Large Magellanic Cloud, more accurately than ever before. This new measurement also improves our knowledge of the rate of expansion of the Universe - the Hubble Constant - and is a crucial step towards understanding the nature of the mysterious dark energy that is causing the expansion to accelerate. The team used telescopes at ESOs La Silla Observatory in Chile as well as others around the globe. These results appear in the 7 March 2013 issue of the journal Nature.
Astronomers survey the scale of the Universe by first measuring the distances to close-by objects and then using them as standard candles to pin down distances further and further out into the cosmos. But this chain is only as accurate as its weakest link. Up to now finding an accurate distance to the Large Magellanic Cloud (LMC), one of the nearest galaxies to the Milky Way, has proved elusive. As stars in this galaxy are used to fix the distance scale for more remote galaxies, it is crucially important.
But careful observations of a rare class of double star have now allowed a team of astronomers to deduce a much more precise value for the LMC distance: 163 000 light-years. 
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Blobrana


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Title: Determining distances using asteroseismic methods
Authors: V. Silva Aguirre, L. Casagrande, S. Basu, T. L. Campante, W. J. Chaplin, D. Huber, A. Miglio, A. M. Serenelli, KASC WG#1

Asteroseismology has been extremely successful in determining the properties of stars in different evolutionary stages with a remarkable level of precision. However, to fully exploit its potential, robust methods for estimating stellar parameters are required and independent verification of the results is needed. In this talk, I present a new technique developed to obtain stellar properties by coupling asteroseismic analysis with the InfraRed Flux Method. Using two global seismic observables and multi-band photometry, the technique determines masses, radii, effective temperatures, bolometric fluxes, and thus distances for field stars in a self-consistent manner. Applying our method to a sample of solar-like oscillators in the Kepler field that have accurate Hipparcos parallaxes, we find agreement in our distance determinations to better than 5%. Comparison with measurements of spectroscopic effective temperatures and interferometric radii also validate our results, and show that our technique can be applied to stars evolved beyond the main-sequence phase.

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Blobrana


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Title: Building the cosmic distance scale: from Hipparcos to Gaia
Authors: Catherine Turon, Xavier Luri, Eduard Masana

Hipparcos, the first ever experiment of global astrometry, was launched by ESA in 1989 and its results published in 1997 (Perryman et al., Astron. Astrophys. 323, L49, 1997; Perryman & ESA (eds), The Hipparcos and Tycho catalogues, ESA SP-1200, 1997). A new reduction was later performed using an improved satellite attitude reconstruction leading to an improved accuracy for stars brighter than 9th magnitude (van Leeuwen & Fantino, Astron. Astrophys. 439, 791, 2005; van Leeuwen, Astron. Astrophys. 474, 653, 2007).
The Hipparcos Catalogue provided an extended dataset of very accurate astrometric data (positions, trigonometric parallaxes and proper motions), enlarging by two orders of magnitude the quantity and quality of distance determinations and luminosity calibrations. The availability of more than 20000 stars with a trigonometric parallax known to better than 10% opened the way to a drastic revision of our 3-D knowledge of the solar neighbourhood and to a renewal of the calibration of many distance indicators and age estimations. The prospects opened by Gaia, the next ESA cornerstone, planned for launch in June 2013 (Perryman et al., Astron. Astrophys. 369, 339, 2001), are still much more dramatic: a billion objects with systematic and quasi simultaneous astrometric, spectrophotometric and spectroscopic observations, about 150 million stars with expected distances to better than 10%, all over the Galaxy. All stellar distance indicators, in very large numbers, will be directly measured, providing a direct calibration of their luminosity and making possible detailed studies of the impacts of various effects linked to chemical element abundances, age or cluster membership. With the help of simulations of the data expected from Gaia, obtained from the mission simulator developed by DPAC, we will illustrate what Gaia can provide with some selected examples.

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Blobrana


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Title: Surface Brightness Fluctuations as Primary and Secondary Distance Indicators
Authors: John Blakeslee

The surface brightness fluctuations (SBF) method measures the variance in a galaxy's light distribution arising from fluctuations in the numbers and luminosities of individual stars per resolution element. Once calibrated for stellar population effects, SBF measurements with HST provide distances to early-type galaxies with unrivalled precision. Optical SBF data from HST for the Virgo and Fornax clusters give the relative distances of these nearby fiducial clusters with 2% precision and constrain their internal structures. Observations in hand will allow us to tie the Coma cluster, the standard of comparison for distant cluster studies, into the same precise relative distance scale. The SBF method can be calibrated in an absolute sense either empirically from Cepheids or theoretically from stellar population models. The agreement between the model and empirical zero points has improved dramatically, providing an independent confirmation of the Cepheid distance scale. SBF is still brighter in the near-IR, and an ongoing program to calibrate the method for the F110W and F160W passbands of the WFC3 IR channel will enable accurate distance derivation whenever a large early-type galaxy or bulge is observed in these passbands at distances reaching well out into the Hubble flow.

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Blobrana


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Title: Measuring cosmological distances by coalescing binaries
Authors: Ivan De Martino, Salvatore Capozziello, Mariafelicia De Laurentis, Michelangelo Formisano

Gravitational waves detected from well-localised inspiralling binaries would allow us to determine, directly and independently, binary luminosity and redshift. In this case, such systems could behave as "standard candles" providing an excellent probe of cosmic distances up to z <0.1 and complementing other indicators of cosmological distance ladder.

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Title: Globular cluster luminosity function as distance indicator
Authors: M. Rejkuba (ESO, Germany)

Globular clusters are among the first objects used to establish the distance scale of the Universe. In the 1970-ies it has been recognized that the differential magnitude distribution of old globular clusters is very similar in different galaxies presenting a peak at M_V ~ -7.5. This peak magnitude of the so-called Globular Cluster Luminosity Function has been then established as a secondary distance indicator. The intrinsic accuracy of the method has been estimated to be of the order of ~0.2 mag, competitive with other distance determination methods. Lately the study of the Globular Cluster Systems has been used more as a tool for galaxy formation and evolution, and less so for distance determinations. Nevertheless, the collection of homogeneous and large datasets with the ACS on board HST presented new insights on the usefulness of the Globular Cluster Luminosity Function as distance indicator. I discuss here recent results based on observational and theoretical studies, which show that this distance indicator depends on complex physics of the cluster formation and dynamical evolution, and thus can have dependencies on Hubble type, environment and dynamical history of the host galaxy. While the corrections are often relatively small, they can amount to important systematic differences that make the Globular Cluster Luminosity Function a less accurate distance indicator with respect to some other standard candles.

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