Astronomical Spectroscopy

MEGA SHORT REVIEW OF

Astronomical Spectroscopy
P. Massey & M. M. Hanson

A basic astronomical spectrograph contains: a slit on to which focused the light from

the source; a collimator, which would take the diverging light beam and turn it into para-

llel light; a disperser; and a camera that would then focus the spectrum onto the detector.

Spectroscopy is a fundamental tool in astronomy, since allows to determine the chemical

compositions, physical properties and radial velocities of astronomical sources.

There are different kinds of blocking filters in order to achieve the wanted wavelength

observation and avoid order overlapping.

Conventional Long-Slit spectrographs are the most versatile, allowing to take spectra of

bright or faint sources and obtain spatially resolved spectra of extended sources. Some steps

involved in the reduction of Long-slit spectrographs data are as followed: Over scan (20-40

columns on the right side of the chip) must be fitted and subtracted. Trim the blank areas. If

the CCD camera had bias structure, it must be removed. Then, depending either one want to

flux calibrate or normalise the spectrum, one should choose the best flat normalisation. After

this, one must remove the non-uniformity in the spatial direction (slit illumination function)

and identify the sky and the object. After this, one needs to identify and fit the lines to the

pixel number in order to perform the wavelength calibration. Finally, one must normalise

the spectrum (in order to perform abundance analysis or measuring radial velocities) or flux

calibrate (in order to model the spectral energy distribution or determine reddening among

others) the spectrum.

Echelle spectrographs avoids to waste detector area by cross dispersing the various or-

ders, spreading them across the detector. This brings some difficulties of flat-fielding.

Multi-objects spectrometers uses an slit mask containing dozen or even hundreds of slits

(Multi-slit spectrograph) or multi-object fibre positioner (Fiber-fed Bench-Mounted spectro-

graphs) to allow multiple objects observation. Multi-object reduction is basically the same as

mentioned in long-slit spectrographs, but there are some differences. For fibers, sky subtrac-

tion must be done by having some fibers assigned to blank sky. For multi-slits, there will be

a very challenging reduction, since the wavelength coverage of each slitlet will depend upon

its placement in the field.

Fabry-Perots and Integral Field spectroscopy obtain spatially resolved spectroscopy of an

extended source.

When observing with a NIR spectrometer, there must be some changes in the reduction,

since the detectors are different, but mainly it presents significant background radiation and

strong absorption from the Earths atmosphere. In order to remove this features, telluric stan-

dards observations must be made with similar declination to the target object, but to transit

30-60 minutes before or after in order to get similar air masses.

Multiwavelength Observations of Accretion in Low-Mass X-ray Binary Systems

Really short review of this paper (1/2 page!) for my PhD reading list

Multiwavelength Observations of Accretion in Low-Mass X-ray Binary Systems

Robert I.Hynes

Low-Mass X-ray binaries (LMXBs) stars are formed by a X-ray emmiter primary star that can

be a neutron star or a stellar mass black hole and a late type G-M donor star with masses

below 1,5M . In this systems, the compact star accretes material from the donor mostly by

Roche lobe overflow.

LMXBs transients are often ultra-soft spectra and in quiescence are often dominated by

the companion star. All transient systems are recurrent, but not at the same timescale. It is

believed that the outburst are as the disk instability modell, originally developed to explain

dwarf novae outbursts.

Spectral energy distributions of LMXBs have prouf to be persuasive evidence on Black

Holes Jets. About LMXBs light curves, we can say that the simplest optical curve comes from

ellipsoidal variations in quiescence, who take a near sinusoidal form with 2 cycles per binary

orbit and is mostly determined by the system inclination. Superhumps are observed as well,

due disk eccentricity and precession, most likely occurring in black holes systems as these

have more extreme mass ratios than most neutron star LMXBs. Quasi-periodic oscillations,

repeating signals not strictly periodic, are common in LMXB. A transient signal it will manifest as a quasi-periodic oscillation. In eclipsing systems, structure from disk axisymmetry can

be observed. Also, eclipses provides precise constraints on the system inclination with sub-

sequent more accurate parameters derived from it, but there are not known eclipsing black

hole in our Galaxy. It is believed that this might be a selection effect.

LMXBs observation is multiwavenength. The most usual lines present in a LMXB spectra

are the Balmer lines, HeI, HeII(optical and ultraviolet). Besides hydrogen and helium, other

lines seen are NIII, CIII around 4640Å, known as the Bowen blend. This donor star lines are

very useful in luminous systems, have prove being a good tool for mass determination. In

quiescent systems, the period and radial velocity of the secondary are enough to estimate

the mass since Kepler’s third law.

Finally, it is possible to say that for the fully understanding of LMXB not only X-ray obser-

vations are necessary, but also optical and spectroscopic.

Here is the link with the real paper
http://adsabs.harvard.edu/abs/2010arXiv1010.5770H

Un sitio muy bueno para ver anime subtitulado latino

Tiene cosas super buenas, todas para ver online en idioma original, subtituladas al espagnol, HD casi todas... recomendado 100%

Cliquear en el titulo para llegar XD

Attention MagE Users!

If you are using MagE spectrograph in order to do some time resolved observation and you want to use MagE's Python based pipeline (by Dan Kelson), you will have to do an extra step.

MagE's python based pipeline took all of your spectra that have the same header and add them in order to get better S/N.  So if you want to have them one by one, you must change the headers in order that every single spectra is named different and, subsequently will be reduced alone.

cool character's character XD

You should check this page! http://www.galeon.com/dibujosce/

This guy is awsome!

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-=[ Mary Poppins ]=-   
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-=[ Pepe LePew-- You find me irresistible, no? ]=-   

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-=[ Schroeder ]=-   

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Curiosity

Hecho curioso:

Para aquellos que estudian optica y saben que un Interferometro de Fabry-Perot constituido por una placa con dos superficies reflectantes, o dos espejos paralelos altamente reflectantes, tambien se llama Etalon.  Aparentmente, hay un lugar en Francia, Somme, que tambien se llama Etalon e historicamente, su poblacion ha crecido en 44 personas en  30 agnos... lo chistoso es que del 80, que tenia 104 personas, aumento su poblacion a 149 en el 2006...







For the optic students who know that a Fabry-Perot Interferometer, made of a transparent plate with two reflecting surfaces, or 2 parallel highly reflecting mirrors is also called etalon.  There is a place in Somme, France, also named Etalon who's population has growth 44 persons in 30 years... funny thing is that from the 80`s that had 104 inhabitants, increased to 149 in 2006....

Febrero: el mes favorito para nacer

Ayer gracias a San Facebook, vi un gran incremento en el radio de natalidad del 2 de Febrero. Busque en cumplea;os Febrero y habia bastantes mas de los que hay por ejemplo en Agosto y me pregunte: habra un mes favorito para nacer?
Aparentemente muchos cientificos se lo han preguntado, lamentablemente no pude encontrar un estudio Chileno al respecto (acepto sugerencias), pero si uno estadounidense. Ociosamente, me lei gran parte del paper en donde estadisticamente encontraban que el mes favorito para nacer era Agosto y el mas pobre, Abril. Podemos extrapolar que siendo un estudio del hemisferio Norte, en el hemisferio Sur sus equivalentes (segun las estaciones del a;o) serian oh! Febrero y Octubre.... Febrero coincide con mi poco cientifica busqueda de natalidad Chilena!... ahora, lo entrete es que ademas, hay un dia favorito de la semana para nacer en gringolandia: el Martes... Porque el Martes?? que misterio.... Y el menos favorito para nacer es el Domingo y el segundo menos favorito, el Sabado.
Yo naci un viernes, y di a luz un MARTES... NOOOOO maldita estadistica!!!

Explicaciones entretenidas sobre las preferencias de natalidad son bienvenidas, mientras no rayen en la ordinariez. XD

El paper de donde saque esta informacion esta aqui:

www.cdc.gov/nchs/data/nvsr/nvsr50/nvsr50_05.pdf




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LEMNISCATE-LEMNISCATA

Thanks to my office mate, and the search of  her "occasional" word of the day, I found out about this:

LEMNISCATE

In Algebraic geometry lemniscate refers to any of several figure-eight shaped curves (like infinity sign), including the Lemniscate of Bernoulli andLemniscate of Gerono.

Gracias a mi companera de oficina q tiene su "ocasional" palabra del dia, Me entere de esta ^^ :

 LEMNISCATA

En geometria algebraica, la lemniscata se refiere a varias curvas con forma de 8 (como el simbolo infinito), incluyendo la Lemniscata de Bernoulli y la Lemniscata de Gerono.

http://mathworld.wolfram.com/Lemniscate.html

AM CVn Stars:Status and Challenge

If you're interested on Solheim paper and don't want to read it, here is the 1 page review of the review!! LOL

J.-E SOLHEIM paper review:
AM CVn stars are short-period binary stars in which a white dwarf (WD) accretes material from a low-mass donor star. Initially they're detached, but they evolved into semidetached contact under certain conditions. These are among the first possible detectable sources of low frequency gravitational wave (GW) radiation, since their evolution toward shorter periods is driven by angular momentum lost due GW radiation. They also represents the terminal phase of a binary star evolution, as been compact and hydrogen low systems by studying these we can study physics under extreme conditions.

There are 3 possible channels for donor evolution: The WD Channel is when Roche lobe overflow happens between 2 WDs, where the donor star is the smallest and helium rich. For this channel there is a Direct-Impact phase. With small mass ratios, the distance between the WDs become shorter because of GW radiation and the accretion stream hit directly on the accretor's surface. Observation of accretor is possible during this phase.
If The Helium-Star Channel the donor star is the nondegenerate core of a 2.5-5 solar masses star that may be at different stages of He exhaustion in the core at the time of contact. Finally, The Hydrogen Star Channel is the less probable. It happen when in a regular Cataclysmic Variable star, the donor lost most of its hydrogen so it's the remnant of a low-mass main-sequence star.

A possible outcome of AM CVn stars is explosive events, such as SN Ia type or SN .Ia supernova, being SN 2005E, a helium accreting binary WD supernova, a good candidate for the first observed SN .Ia with AM CVn progenitor.

The Am CVn objects can be divided in 4 groups according to disk properties: 1.-Ultrashort periods an no disk (P<12 m), 2.-Large stable disks in superoutburst state (12
<20 m), 3.- Variable-size disk, with outburst and occasional superoutburst (20
<40 m) and 4.- Small stable disk (P>40 m). For the last one, the spectra changes from a high state with absorption lines to a low state with emission lines.

In last 10 years AM CVn stars number had increased because of the large observation campaigns, rising them up to 25 systems. Thanks to this, density and population estimations have improved. There are 2 evolution scenarios: the optimistic case and the pessimistic case. Roelofs et al. predicted sky surface density of Am CVn stars based on T_eff, M_g, Galaxy population models and WD and helium progenitors assumed evolution. The predicted density of AM CVn stars resulted to be highest for low Galactic latitudes, with an error lower than a factor 2. But the predicted density for optimistic case and the pessimistic case are far from reality. This is telling us that something may be overlooked and there still work to be done.

"The strange star SS433 may be a black hole whose accretion disk is highly inclined with respect to its orbit about a companion star. Digital, cover, February 2005 "Astronomy" magazine."

Image used with the permission of Don Dixon, FIAAA
Scientific Illustration

http://cosmographica.com/gallery/portfolio2007/content/index_28.html



Very soon in Spanish as well (hopfully!) XD enjoy