Astrophysics Topics

Absolute flux units and magnitudes

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Meetings

http://www1.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/en/meetings/

Variable star are defined as "stars having an apparent property changing with time" (usually their brightness). These properties can be: - intrinsic: stellar luminosity actually changes (e.g., pulsations); - extrinsic: owing to changes in the amount of light reaching Earth (e.g., eclipses).

All stars have some variation in luminosity. The Sun's luminosity varies about 0.1% over a solar cycle.

The first historical variable star is the Algol system, known nowadays to be a eclipsing binary system. Its variability was record in the old Egypt. In the modern times, it was notes the variability of the Mira star (Omicron Ceti) in 1638.

The famous General Catalogue of Variable Stars was the first list of variable stars created by the Academy of Sciences of the USSR, and continuously been updated by Russian researchers. In 2008, 46000 variable stars were known in the Milky Way, 10000 in other galaxies and a list of 10000 candidates exist.

The variabilities are classified as photometric or spectroscopic. They can be Periodical, Semiperiodical, Irregular or Unique. Examples: changes in velocities (spec. shifts) are a signal of binary system; abnormal emission or absorption lines indicate circumstellar activity and/or magnetic field...

Chart

Dr Ashley J. Ruiter (@growzchilepeps): "Chien-Hsiu Lee explains the work being done by ANTARES to make sure current ZTF and future LSST data are distributed for the optimal (for those data) streams (research interests). #iaus357 @LSST @ztfsurvey I am learning about brokers! :)"

Nomenclature

In a given constellation, the first variable star discovered were designates with the letter R (and continuously until Z). Then, RR...*RZ*, SS...*ZZ*. Then AA...*AZ*, BB...*QZ*, with J omitted. After exhausted the total of 334 possibilities, stars as V335, V....

The subgroups of variabilities are divided according to their prototype.

Intrinsic variabilities

Pulsation, Eruption, Cataclysmic/Explosive...

Pulsation

Radial or non-radial
Fundamental frequency (f₀) determining the period.
- Harmonic or overtone (n > 1)
It the variability has a complex shape (no clear frequencies), it is called irregular or stochastic.

The modes of pulsations can be:

p-mode = pressure (or acoustic) mode, driven by internal pressure fluctuations within a star; their dynamics being determined by the local speed of sound. Shape: reflections at stellar surface.
g-mode = gravity mode, driven by buoyancy (aka restoring force). Shape: elliptical movements around the stellar core.
f-mode = surface gravity modes. Shape: akin to ocean waves along the stellar surface.

Extrinsic variabilities

Eclipsing, multiple stars (rv)
Rotating variables ("spots")

Shape missions

MOST
CoRoT
WIRE
SOHO (exclusive to the Sun)
Kepler
BRITE (a constellation of six nanosatellites. Sizes: cube os 20 cm!)

Peculiar stars

Excellent reference is http://www.astrosurf.com/buil/us/peculiar.htm, were there are lists of bright Bp/Ap and Herbig Be/Ae stars.

Astrophysical disks

http://www.damtp.cam.ac.uk/user/hl278/DAD.html

Observational

mes	RA0	RAm	RAf
Jan	00	08	16
Fev	02	10	18
Mar	04	12	20
Abr	06	14	22
Mai	08	16	00
Jun	10	18	02
Jul	12	20	04
Ago	14	18	06
Set	16	00	08
Out	18	02	10
Nov	20	04	12
Dez	22	06	14

ESO Periods

Period Odd - 01 Apr to 30 Sep (RA limits: ~10h to ~02h)

deadline ~ 01 Oct
Period Even - 01 Oct to 31 Mar (RA limits: ~22h to ~14h)

deadline ~ 01 Apr

OPD Periods

Período Verão - 01 set a 28* fev (RA limits ~20h a ~12h)

Limite ~ 30 abr
Período Inverno - 01 mar a 31 ago (RA limits: ~08h a ~00h)

Limite ~ 31 oct

Spectro-astrometry

The spectro-astrometric technique is a method for studying the spatial structure of astronomical sources on scales well below the normal limit on resolution set by the seeing disk size or the diffraction limit. It relies on the fact that the relative position of a source at two or more wavelengths can be measured to an accuracy limited only be photon statistics, if the measurements are simultaneous.

The technique is being used for the study of structure in pre-main-sequence stars, where it can be used to detect binary companions and to study the outflows from the stars. It is also being used to study the structure of the narrow line region in active galactic nuclei.

About fluxes and conversions

The relation of Black Body curves are:

I(λ, T)dλ = I(ν, T)dν

And convertion of units:

[Y erg/cm^2/s/Hz]dHz = [X1 erg/cm^2/s/A]dA
dHz/dA = "(c/A)'dA" = -c/(A)^2
[Y erg/cm^2/s/Hz] = dA/dHz * [X1 erg/cm^2/s/A]
[Y erg/cm^2/s/Hz] = (1/c) * [X2 A]^2 * [X1 erg/cm^2/s/A]
# c = 3e18 A/s
[Y erg/cm^2/s/Hz] = 3.335641e19 * [X2 A]^2 * [X1 erg/cm^2/s/A]

# Hdust models: (ergs/s/cm2/mu) * 1e-4 = (ergs/s/cm2/A)

Interferometers

ESO interferometers

VINCI: First VLTI generation. ? BAND, 2 telescopes, ? resolution
MIDI: Second VLTI generation. ? BAND, 2 telescopes, ? resolution
AMBER: JHK bands, 3 telescopes. R=(30?, 1500 and 12000) resolution modes. PROBLEMS with absolute visibilities calibration.
PIONIER: H band. 4 telescopes. 3, 9 channels (resolution)
MATISSE: ?
GRAVITY: ?