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TOPIC: Determining Distance
Blobrana


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Cosmological distance indicators
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Title: Cosmological distance indicators by coalescing binaries
Authors: Mariafelicia De Laurentis, Salvatore Capozziello, Ivan De Martino, Michelangelo Formisano

Gravitational waves detected from well-localised inspiralling binaries would allow to determine, directly and independently, both 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 thus complementing other indicators of cosmological distance ladder.

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Earth-Sun distance
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Title: Measuring the Earth-Sun distance during a lunar eclipse
Authors: Costantino Sigismondi

The classical method for measure the Earth-Sun distance is due to Aristarchus and it is based upon the measure of the angle Moon-Earth-Sun when the Moon is exactly in quadrature. Such an angle is only 9 arcminutes smaller than 90 degrees, and it is very difficult to evaluate, being necessary to look directly towards the Sun. The distance Earth-Moon and the Earth's diameter are necessary ingredients in order to derive the value of the astronomical unit. This method requires also the knowledge of the Moon's distance and the Earth's diameter, but it can permit a more precise measurement of the involved angles.

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Blobrana


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Universal Distance Scale
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Title: Anchoring the Universal Distance Scale via a Wesenheit Template
Authors: Daniel J. Majaess, David G. Turner, David J. Lane, Arne Henden, Tom Krajci

A VI Wesenheit diagram featuring SX Phoenicis, delta Scuti, RR Lyrae, type II and classical Cepheid variables is calibrated by means of geometric-based distances inferred from HST, Hipparcos, and VLBA observations (n=30). The distance to a target population follows from the offset between the observed Wesenheit magnitudes and the calibrated template. The method is evaluated by ascertaining the distance moduli for the LMC (mu_0=18.43±0.03 se) and the globular clusters Omega Cen, M54, M13, M3, and M15. The results agree with estimates cited in the literature, although a nearer distance to M13 is favoured and observations of variables in M15 suffer from photometric contamination. A Wesenheit template of the LMC can be employed since that galaxy exhibits precise OGLE data for variables of differing classes, that includes recent observations for delta Scuti variables indicating the stars follow a steeper VI Wesenheit function than classical Cepheids pulsating in the fundamental mode. VI photometry for the calibrators is tabulated to facilitate further research, and includes new observations acquired via the AAVSO's robotic telescope network (e.g., VY Pyx: <V>=7.25 and <V>-<I>=6.58). The approach outlined here supersedes the lead author's prior first-order effort to unify variables of the instability strip in order to establish distances.

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Blobrana


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RE: Determining Distance
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Ohio State University researchers have found a way to measure distances to objects three times farther away in outer space than previously possible, by extending a common measurement technique.
They discovered that a rare type of giant star, often overlooked by astronomers, could make an excellent signpost for distances up to 300 million light years -- and beyond.
Along the way, they also learned something new about how these stars evolve.
Cepheid variables -- giant stars that pulse in brightness -- have long been used as reference points for measuring distances in the nearby universe, said Jonathan Bird, doctoral student in astronomy at Ohio State. Classical cepheids are bright, but beyond 100 million light years from Earth, their signal gets lost among other bright stars.
In a press briefing at the American Astronomical Society meeting in Pasadena, CA, Bird revealed that a rare and even brighter class of cepheid -- one that pulses very slowly -- can potentially be used as a beacon to measure distances three times farther than their classical counterparts.

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Blobrana


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Radio telescopes extend astronomy's best 'yardstick'
Radio astronomers have directly measured the distance to a faraway galaxy, providing a valuable "yardstick" for calibrating large astronomical distances and demonstrating a vital method that could help determine the elusive nature of the mysterious Dark Energy that pervades the Universe.

"We measured a direct, geometric distance to the galaxy, independent of the complications and assumptions inherent in other techniques. The measurement highlights a valuable method that can be used to determine the local expansion rate of the Universe, which is essential in our quest to find the nature of Dark Energy" - James Braatz, of the National Radio Astronomy Observatory (NRAO), who presented the work to the American Astronomical Society's meeting in Pasadena, California.

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Blobrana


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TRGB
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Title: The Tip of the Red Giant Branch
Authors: M. Bellazzini (INAF-Oabo)
(13 Nov 2007)

I review the latest results on the calibration of the Tip of the Red Giant Branch as a standard candle, in the optical and in the near infrared. The agreement among different and independent empirical calibrations is rather good, if all the uncertainties are taken into account. The possible extension of the calibration to SDSS photometric bands (i,z) is also discussed.

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Blobrana


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The Tip of the Red Giant Branch
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Tip of the red giant branch (TRGB) is a primary distance indicator used in astronomy. It uses the luminosity of the brightest red giant branch stars in a galaxy to gauge the distance to that galaxy. It has been used in conjunction with observations from the Hubble Space Telescope to determine the relative motions of the Local Cluster of galaxies within the Local Supercluster.
The TRGB indicator uses stars in the old stellar populations (Population II).

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Blobrana


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RE: Determining Distance
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HR Diagram-Stars



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Blobrana


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Evolució (Evolución - Evolution)
Cepheid Variables


Hubble Space Telescope Measures Precise Distance to the Most Remote Galaxy Yet

The Cepheids


Henrietta Leavitt discovered the relation between the period and luminosity of cepheid variable stars. By using Henrietta's discovery, astronomers can estimate the distances to these stars and thus to their home galaxies. Her discovery became one of the foundations of modern cosmology.

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Blobrana


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Hertzsprung Russell diagrams and cepheid variables to estimate distance in astronomy


Use of HR diagrams and cepheid variables are well tried techniques for the estimation of distance in astronomy and have been used as a basis of comparison for other methods. The video explains the basis of both techniques.

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