Tag Archive for 'stellar cartography'

[Stellar Mapping] Brown Dwarf dataset added, plus some major updates!

I’ve added a new Brown Dwarf dataset to the Stellar Mapping page (thanks to LiNeNoiSe for pointing this out to me)! This should hopefully be the last major update to the stellar datasets for a while – the next project on the list is to figure out what the reworked Arms for 2300AD might look like based on the realistic data.

The new catalogue is the LDwarf dataset – this is a list of brown dwarfs taken from the IPAC Brown Dwarf Archives (this dataset was last updated on 14 Feb 2011). It is not a complete list of all known brown dwarfs – these are the only the ones for which parallax data is provided there.

L Dwarf dataset, looking Corewards

While some of the distances presented in this dataset are derived from trigonometric parallaxes, others are derived instead from (spectro)photometric parallaxes. Trigonometric parallaxes are derived by measuring the angular shift of a star relative to the background stars as the earth moves around the sun on its orbit (the stellar distances in the HIPX, RECONS and other datasets here are derived using this method) – these are generally more accurate than photometric parallaxes. “Photometric parallaxes” are techically not really “parallaxes” at all – instead the spectral type of the object is checked against luminosity models to get an estimate of its luminosity, which is used along with the observed visual/IR magnitude to calculate the distance to the object. Unfortunately this method is not very precise, and some of the photometric parallaxes for these objects in the LDwarf dataset have very large error bars – but this is the best data that is currently available.

One of these systems – SDSS J141-134 – is listed in the original data as having a (photometric) parallax of 127 +/- 27 mas. This places it almost in the right location to allow a 7.7 ly link between Xi Bootis and CE Bootis, which would be very useful in the 2300AD setting. I have changed its parallax to 122 mas on this list (which is comfortably within its error bars, and allows it to connect those two stars and link to the stars around Arcturus). The original (127 mas) data for this system is listed in the text file in the LDwarf.zip file if it’s needed.

It should also be noted that two Brown Dwarfs (UGPS J072227.51-054031.2 and DENIS J081730.0-615520) are located within the RECONS sphere. These are not listed in the RECONS data, but are retained here since their parallaxes indicate that they are within 22.8 lightyears of Sol (even given their large error bars). They do not make a significant difference to the 2300AD route distribution.

Some of the Brown Dwarfs in this list are members of multiple systems that are listed in other datasets presented on this site. These are listed as complete multiple star systems on this list (the other components are duplicated here using the original data) – the datasets should merge seamlessly when combined (the ID numbers are preserved in both lists) but some components may be duplicated – this should not create problems since they will have the same name and position.

Other Updates

I’ve also made several other updates to the datasets, so you’ll need to download them again to get the latest versions!

  • The Pleiades Corridor has been updated to use Extended Hipparcos data.
  • The Yale and Gliese 3 Historical Datasets have been moved into a blog article to separate them from the more accurate datasets on the Stellar Mapping page.
  • The Extended Hipparcos and CTIOPI datasets have been updated to include Multiple Systems. A and B components of some of the multiple stars in the original data were separated by several lightyears due to parallax inconsistencies – these were listed separately, but now they have been combined nto Multiple star systems that are located at the XYZ co-ordinates of the original A component.
  • The Further Stars list is still using New Reduction Hipparcos (and other) data. I will be updating it to HIPX at a later date, but it does contain duplicate stars in different positions and should be considered to be less accurate than the other datasets!
  • [Stellar Mapping] Historical Datasets (Yale & Gliese3)

    As part of this weekend’s update to my Stellar Mapping page (more details about that will be in the next post), I’ve decided to move the Historical datasets (Yale and Gliese3) onto a blog post since they’re no longer accurate and probably aren’t being used much anyway (there’s a link from the Stellar Mapping page to this blog post). So, here they are!

    Historical Datasets

    Historical databases should not be considered “accurate” by modern standards, and have been largely superseded by the ones listed in the “Accurate Datasets” section. The full Yale and Gliese catalogues have been clipped at 300 ly from Sol.

    Yale Trigonometric Parallaxes, Fourth Edition: The Yale catalogue (a.k.a the General Catalogue of Trigonometric Parallaxes, or GCTP) is a historical dataset that was one of the most accurate near star catalogues before Hipparcos, with parallax measurements taken from the ground-based observations. It includes many fainter stars that are not in the Hipparcos catalogue, but the distance accuracy is much lower. It also include many stars that are in the Hipparcos catalogue, but because of the lower accuracy they are somewhat shifted from their Hipparcos-derived positions – the difference increases with distance from Sol. However, the Yale catalogue does include Spectral data for most stars. As such, the Yale and Hipparcos catalogues should NOT be combined.

    Source: http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=I/238A/picat.
    Number of star systems: 6,051
    Distance range: 22.8 – 300 lightyears from Sol.
    Accuracy: Positional data are less accurate than Hipparcos, but spectral data is included. Physical data are not accurate. All stars are listed as single stars.

     

    Gliese Nearby Stars, Preliminary 3rd Version: The Gliese catalogue is one of the “classic” historical star catalogues – it was updated in 1991, and includes all stars known at the time within 25 pc of Sol, and a few that are further out. It has low accuracy, but again includes some of the dimmer stars that Hipparcos does not include. The 2300AD star map is apparently based on the 2nd version of this catalogue.

    Source: http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=V/70A.
    Number of star systems: 3,667
    Distance range: 22.8 – 300 lightyears from Sol.
    Accuracy: Positional data are less accurate than Hipparcos, but spectral data is included. Physical data are not accurate. All stars are listed as single stars.

    [Stellar Mapping] Extended Hipparcos dataset added!

    I’ve now replaced the New Reduction Hipparcos data with the new Extended Hipparcos (HIPX) dataset published in 2012 by Anderson & Francis (see this paper for all the details). The HIPX dataset expands the original dataset to include luminosities, spectral types and much more useful astronomical data from a variety of sources, making this the definitive source of information about these stars! The searchable online HIPX catalogue is located at http://vizier.u-strasbg.fr/viz-bin/VizieR-3?-source=+V/137A/XHIP.

    The HIPX data replaces the New Reduction Hipparcos data on this website – Astrosynthesis and Galactic XYZ data have both been updated! In most cases the HIPX XYZ data is identical to the New Reduction Hipparcos XYZs, but issues with the parallaxes for some of the multiple systems in the New Reduction data led to significant inaccuracies there – in those cases, the parallaxes were reverted back to the original Hipparcos parallax data (again, refer to the XHIP paper for further explanation).

    The XHIP data includes more star names (including common/arabic names), which are also presented here. However, note that Gliese numbers higher than 3000 have been removed for ease of reference. Technically these numbers aren’t “Gliese numbers”, they’re “NN” or “Wo(oley)” numbers. Because this could cause confusion, I decided to remove them instead of editing them all, but this isn’t a huge loss since the stars can still be tracked using their HIP numbers or other names.

    If you’ve been using the New Reduction data, then be sure to head over to my Stellar Mapping page to download the new Extended Hipparcos dataset!

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    In other news, my Stellar Mapping page now has the Atomic Rockets Seal of Approval! This is Winchell Chung’s way of saying that he likes my work, and I’m very happy about that because I’ve been a fan of his Atomic Rockets website pretty much since it first appeared online (it’s a great resource for any SF fan)! His 3D Starmaps site is also one of the main inspirations for my own stellar mapping efforts! Thanks, Winchell! 🙂