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I am completely new to astrophysics and currently writing a paper on Cepheid variables for high school physics.
I would like to filter out all Cepheid variables in the local system which I would ideally query in python using astroquery. I find the Cepheid variables using
otypeand wanted to ask what the most efficient (in terms of putting minimum strain on the database) way to specify the local group would be.
Also, what are the coordinates for the local group I can use for a query in this style:
'region(circle, gal, 123.5 -17.8, 0.5d)'?
ADQL Cheat sheet
All information about ADQL are available at this IVOA Document. This page gathers minimal ADQL features required to interrogate Simbad-TAP. These features are explained through query examples on the following Simbad tables:
1. Minimal queries
2. Labeling columns
In the output of a query execution, columns are identified by their name in the database (i.e. ra , dec and main_id ). However, these output names can be changed while writing the query:
=> Output column names will be: ra , dec and Usual ID .
3. Rows limit
Select the 50 first rows of the table basic .
4. Ordering rows
- Order by column name
- Order by column label
- Order by column index
- Order by descending column name
5. Filtering rows
6. Geometrical functions
ADQL also allows interrogation on position like Search Cone.
In this example only two types of regions have been used:
- POINT(coord_sys, right_ascension, declineason)
- CIRCLE(coord_sys, ra_center, dec_center, radius_in_degree)
But the following regions also exist:
- BOX(coord_sys, ra_center, dec_center, width_in_degrees, height_in_degrees)
- POLYGON(coord_sys, ra_vertice1, dec_vertice1, ra_vertice2, dec_vertice2, ra_vertice3, dec_vertice3 [, . ])
- REGION(stc_region) (not implemented in Simbad-TAP)
The two main geometrical functions of ADQL are:
- CONTAINS(region1, region2)
- INTERSECTS(region1, region2)
These functions return 1 if region1 contains/intersects region2, 0 otherwise.
ADQL also provides functions to compute distance, area, .
- DISTANCE(POINT1, POINT2)
- COORDSYS(region) (not implemented in Simbad-TAP)
- CENTROID(region) (not implemented in Simbad-TAP)
7. Using several tables (Join)
8. Multi Ordered Coverage output
9. Upload tables
In TAP, you can upload VOTables and interrogate them as tables in an ADQL query. When uploading a VOTable, a table name must be provided. This name prefixed by TAP_UPLOAD must be used to reference the table in the ADQL query
10. Simbad specific features
You can find this information in the column sptype of the table basic . You can filter objects by their spectral type with the following operators: = , != , < , <= , > , >= , BETWEEN '..' AND '..' , IN and NOT IN .
This information is available in the columns otype, otype_txt of the table basic . You can filter objects by their type with the following operators: = , != , IN and NOT IN . Since object types can be more or less precise (for instance: AGN are particular types of Galaxy), you can specify if you search for a precise type of object or for its descendants by adding 2 points ( '..' ) at the end of the type name:
This information is available in the column main_id of the table basic and especially in the column id of the table ident .
GAIA - Graphical Astronomy and Image Analysis Tool
GAIA is an highly interactive image display tool but with the additional capability of being extendable to integrate other programs and to manipulate and display data-cubes. At present image analysis extensions are provided that cover the astronomically interesting areas of aperture & optimal photometry, automatic source detection, surface photometry, contouring, arbitrary region analysis, celestial coordinate readout, calibration and modification, grid overlays, blink comparison, image defect patching, polarization vector plotting and the ability to connect to resources available in Virtual Observatory catalogues and image archives, as well as the older Skycat formats.
GAIA also features tools for interactively displaying image planes from data-cubes and plotting spectra extracted from the third dimension. It can also display 3D visualisations of data-cubes using iso-surfaces and volume rendering.
Specialised handling of data from the CUPID package provides the visualisation of clumps of emission in 2D and 3D, as ellipses, polygons and boxes. This supports the inspection of JCMT science archive advanced data products.
Interoperability with other SAMP enabled applications is provided so that GAIA can be used as part of a integrated desktop (usually querying the Virtual Observatory).
GAIA is a derivative of the Skycat catalogue and image display tool, developed as part of the VLT project at ESO. Skycat and GAIA are free software under the terms of the GNU copyright.
The 3D facilities in GAIA use the VTK library.
What can it do?
The capabilities of GAIA fall roughly into four areas those of an image display tool, those provided for the analysis of images, those for querying on-line resources (catalogues of images and data) and cube handling. Each of these areas is described very briefly in the next lists:
- Image Display Capabilities
- Display of images in FITS and Starlink NDF formats.
- Panning, zooming, data range and colour table changes.
- Continuous display of the cursor position and image data value.
- Display of many images.
- Annotation, using text and line graphics (boxes, circles, polygons, lines with arrowheads, ellipses. ).
- Real time pixel value table.
- Display of image planes from data cubes.
- Display of point and region spectra extracted from cubes.
- Display of images and catalogues from SAMP-aware applications.
- Selection of 2D or 3D regions using an integer mask.
- Aperture photometry.
- Optimal photometry.
- Automated object detection.
- Extended surface photometry.
- Image patching.
- Arbitrary shaped region analysis.
- Polarization vector plotting and manipulation.
- Blink comparison of displayed images.
- Interactive position marking.
- Celestial co-ordinates readout.
- Astrometric calibration.
- Astrometric grid overlay.
- Celestial co-ordinate system selection.
- Sky co-ordinate offsets.
- Real time profiling.
- Object parameterization.
- VO capabilities
- Cone search queries
- Simple image access queries
- Plot positions in your field from a range of on-line catalogues (various, including HST guide stars).
- Query databases about objects in field (NED and SIMBAD).
- Display images of any region of sky (Digital Sky Survey).
- Query archives of any observations available for a region of sky (HST, NTT and CFHT).
- Display positions from local catalogues (allows selection and fine control over appearance of positions).
- Display of image slices from NDF and FITS cubes.
- Continuous extraction and display of spectra.
- Collapsing, animation, detrending, filtering.
- 3D visualisation with iso-surfaces and volume rendering.
- Celestial, spectral and time coordinate handling.
- Display catalogues in 2 or 3D
- Display selected regions of masks in 2 or 3D
The latest version of GAIA is available in the EAO Starlink release.
Once installed you should be able to view the documentation (SUN/214) that came with GAIA using the command:
To start using GAIA look at the "Getting Started" section. On-line help is available in the "Help" menu.
If you'd like further help, or would like to get some ideas for using GAIA more effectively, then try the GAIA Cookbook (SC/17).
GAIA is currently at version 4.4-4, which is part of the
release. The changes in this release are described in the current news file.
The following information about GAIA is available on-line:
A lot of pretty pictures and walkthoughs are also available in the GAIA Index side box.
Re-current problems and bugs
Unresponsive toolboxes on laptops
There seems to be a recurrent issue setting up laptops to run GAIA The symptoms of this are that GAIA may refuse to start up, may hang when using some of the toolboxes, or may refuse to respond to remote requests. The problem is that the local networking isn't working correctly due to a misconfiguration of the /etc/hosts file. This should contain a line like:
Importing astroquery on its own doesn't get you much: you need to import each sub-module specifically. Check out the docs to find a list of the tools available. The API shows the standard suite of tools common to most modules, e.g. query_object and query_region .
To report bugs and request features, please use the issue tracker. Code contributions are very welcome, though we encourage you to follow the API and contributing guidelines as much as possible.
Aladin Desktop & Aladin Lite use reprocessed data based on HiPS technology (Hierarchical Progressive Survey) with the capability to zoom and pan on any regions of the surveys. There are about 550+ HiPS surveys available for 250TB of pixels provided by several collaborative servers.
Aladin Desktop provides direct data access to most of the astronomical servers over the world (CDS, NED, ESO, CADC, MAST, HEASARC, NRAO, ROE, IMCCE, etc), and obviously, local user data.
Filtering local region in SIMBAD - Astronomy
It is a significant problem to determine the shape and extent of our galaxy from our point of view inside it. On a clear night with a dark sky, the band of stars and dust that make up the Milky Way can be easily seen, but when mapped over the whole sky in optical light, it has a complicated appearance that does not represent its real shape.
The first attempts to determine the shape of our galaxy, called the Milky Way Galaxy were through simply counting stars. Sir William Herschel made the first systematic star count in the 1780's, later expanded by Jacobus Kapteyn the early 1920's. Both of these attempts ignored interstellar extinction (the dimming of starlight by dust), and concluded that the Sun resides near the center of a flat, pancake-shaped distribution of stars.
However, between 1915 and 1919, Harlow Shapley estimated the distances to globular clusters, using RR Lyrae and Pop II Cepheid variables as distance indicators. He found that many more clusters where seen in the direction of Sagittarius, and concluded that globular clusters are distributed uniformly around our galaxy. The concentration in the direction of Sagittarius was due to the fact that our Sun is off-center within the galaxy, and the center is in the direction of Sagittarius.
We can now obtain images in the infra-red region of the spectrum, which can penetrate dust easily. When we image the entire sky in the infra-red, as was done with the COBE satellite, we obtain the much clearer picture of the Milky Way Galaxy shown below.
Image of the Milky Way Galaxy taken with the COBE satellite. Note that now we can see through the dust to the central bulge , and the disk appears much more uniform. Below are several views of the Milky Way seen in various wavelengths.
- Most of the stars of the galaxy reside in a disk , which closely resembles the disks of spiral galaxies seen elsewhere in the sky. Also in the disk are gas clouds , dust , and very young stars ( O-B associations ). The stars tend to have high metallicity (Z > 0.01).
- There is a central bulge of stars near the center of the galaxy that is more spherical in shape. The stars here are older (and redder) than the disk population.
- Globular clusters are distributed in an approximately spherical halo above, below, and within the disk. A small number of high-velocity stars are also seen in this halo region. The stars here are very old, and typically have low metallicity (Z < 0.001)
- radial velocity (from doppler shifts of spectral lines) and
- tangential velocity (from proper motion).
Example: For star Gl 4.2A, above, we have m "= 0.592 and p "= 0.0483 , so v q = 58.1 km/s. The radial velocity is shown in the table to be v r = 2.6 km/s , so the total velocity, or space velocity is v= (v r 2 + v q 2 ) 1/2 = 58.2 km/s.
The quantities in the table, however, are not so simple to measure. To convert proper motion to velocity, one must know the distance, which means either measuring a trigonometric parallax (which is impossible for all but the nearest stars) or using a spectroscopic parallax. In addition, the proper motion must be measured. For nearby stars, the proper motion can be quite large, but for distant stars it can be very small. Luckily, we can monitor stars over many decades, after which the proper motion accumulates and can be measured.
Radial velocity is easier, since it is determined from spectral line shifts, which can be seen at any distance (as long as the star is bright enough). However, for both radial velocity and proper motion one must subtract other motions such as the Earth around the Sun (
30 km/s), and the Sun's own motion through space (
19.5 km/s--our text gives 16.5 km/s). Galactic Coordinates
- Before we can go further with stellar motions, we need to define a coordinate system in which to make our measurements. Since we expect the galaxy to rotate about its center, and all of the objects that make up the galaxy should orbit this center in Keplerian orbits, we could form a coordinate system that is galactocentric , and for some cases that is the appropriate system to use. However, since we are observing from our location in the galaxy, a second coordinate system centered on the Sun will prove more useful. This coordinate system is called simply galactic coordinates . As viewed from the Sun, coordinates in the galactic plane are at galactic latitude b = 0 o , while at the galactic poles (N or S), the galactic latitude is b = 90 o . Galactic longitude l is measured from the center of the galaxy (the Sagittarius region) as shown in the figure below.
- cos b cos (l - 33 o ) = cos d cos ( a - 282.25 o )
cos b sin (l - 33 o ) = cos d sin ( a - 282.25 o ) cos 62.6 o + sin d sin 62.6 o (from celestial to galactic)
sin b = sin d cos 62.6 o - cos d sin ( a- 282.25 o ) sin 62.6 o
- Stars share the general rotation of the galaxy.
- Stars have their own peculiar motions superimposed on this general rotation.
- The average velocity (magnitude and direction) of stars in the local solar neighborhood should be zero with respect to this general rotation.
- The Sun may have a motion relative to the general rotation.
- u = P - P LSR = P
v = Q - Q LSR = Q -Q o
w = Z - ZLSR = Z
- We mentioned before that the stars should orbit the galaxy in Keplerian orbits. For Keplerian orbits, we expect Kepler's Third Law to hold:
- P 2 = (4 p 2 /GM)R 3
P = 2 p R / V
- V = (GM/R) 1/2
- V = (GM(R)/R) 1/2 = G(4 p R 2 r /3) 1/2
Grab some data from ALMA, then analyze it using the Spectral Cube package after identifying some spectral lines in the data.
Find ALMA pointings that have been observed toward M83, then overplot the various fields-of view on a 2MASS image retrieved from SkyView. See http://nbviewer.jupyter.org/gist/keflavich/19175791176e8d1fb204 for the notebook. There is an even more sophisticated version at http://nbviewer.jupyter.org/gist/keflavich/bb12b772d6668cf9181a, which shows Orion KL in all observed bands.
Filtering local region in SIMBAD - Astronomy
Millimeter-wave observations made toward the NGC 6530-M8 star-forming complex are compared with high-quality optical interference-filter photographs of that region. Extensive CO observations reveal a large molecular cloud in this direction, within which three bright spots of CO emission are found. Two bright spots are associated in angle with prominent optical features. One of these is coincident with the star Herschel 36 and the Hourglass Nebula the second appears coincident in angle with an ionization front southeast of Herschel 36. The kinematics of the molecular cloud is studied. The radial velocity of CO emission is found to vary smoothly across the cloud, but it is difficult to interpret this in terms of coherent mass motion of the entire cloud. Analyses of CO, radio-continuum, and optical data indicate that Herschel 36 is the most likely ionizing source for most of the M8 II region. Comparison of optical and radio observations suggests a geometrical model for the region, which places the H II region at the front edge of the molecular cloud. Further considerations indicate that the M8 molecular cloud, the M8 H II region, the young cluster NGC 6530, and the Sgr OB1 association appear to be related in a geometrical evolutionary sequence with cloud evolution, and possibly star formation, proceeding inward with time from the position of the foreground star cluster to the position of the molecular cloud.
Not the only North Star
There is a famous Shakespeare quote that has Julius Caesar stating, "I am constant as the northern star." But in reality, Polaris is not really constant, at least over a time span measured over centuries, for it will not always be our North Star.
Like a spinning top that wobbles due to a force called torque, our spinning earth is also subject to torque that is caused by the gravitational forces of the sun and moon. As a result the earth's axis wobbles (called precession), and as a consequence describes a circle in the sky the gradual change in the direction of the earth's axis in space.
Filtering local region in SIMBAD - Astronomy
Emission-line strengths have been obtained at 10 positions in the outer regions of the 30 Dor nebula and analyzed in the standard way. There are two major results: (1) the elemental abundances for nine of the outer regions are remarkably similar to those previously measured in the core. This result implies the spectra of the cores and halos of giant H II regions (subject to the different ionizing radiation fields) are analyzed correctly by the standard methods. Hence measurements of extragalactic H II regions with poor spatial resolution correctly represent the abundances of the whole nebula. The O/H ratio in 30 Dor, by number, is 0.30 solar. The Ne/O, S/O, Ar/O, and Cl/O are close to solar. The gas-phase Fe/O is about 0.2 solar, which probably implies that most of the iron is within solid grains. The He/H is 0.0810 as shown by each of the three strong lines available. One region is cool and rich in helium and all other heavy elements except nitrogen. The spectrum of the region does not resemble that of a supernova remnant in that the forbidden O I and S II lines are not nearly strong enough. The abundances can be explained fairly well as over 10 solar masses of H-poor material ejected during the evolution of a single massive (about 80 solar masses) star during its late O-star and Wolf-Rayet phases.
Watch the video: Sinbad helps himself to some choice wine (June 2022).