Near stars and their planets

日本語

Two imports hold the stars that are worth travelling to. @johnmorrisdotca/hoshi-stars/near-stars is the 73 star systems within 20 light-years: Alpha Centauri with Proxima, Barnard's Star, Wolf 359, Sirius and the rest. @johnmorrisdotca/hoshi-stars/exoplanet-hosts is the 80 host stars of confirmed planets that matter to a visitor, with each planet's name and orbital period. Each is its own import (about 6 kB and 9 kB gzipped), so a page that does not need them pays nothing. Both are pure: no DOM, no clock.

import { exoplanetHostByName } from "@johnmorrisdotca/hoshi-stars/exoplanet-hosts";
import { nearStarByName, nearStars } from "@johnmorrisdotca/hoshi-stars/near-stars";

const near = nearStars();
console.log(`${near.length} systems within 20 light-years, the nearest ${near[0].name}`);

const barnard = nearStarByName("Barnard's Star");
console.log(`${barnard.name} (${barnard.nameJa}): ${barnard.lightYears.toFixed(2)} light-years, ${barnard.spectralType}`);
console.log(`position from ${barnard.sources.position}, distance from ${barnard.sources.distance}, ${barnard.constellation}`);

const trappist = exoplanetHostByName("TRAPPIST-1");
console.log(`${trappist.name}: ${trappist.planetCount} planets, periods ${trappist.planets.map((p) => p.periodDays.toFixed(2)).join(", ")} days`);

73 systems within 20 light-years, the nearest Alpha Centauri
Barnard's Star (バーナード星): 5.98 light-years, M5 V
position from 2MASS, distance from GCTP, Oph
TRAPPIST-1: 7 planets, periods 1.51, 2.42, 4.05, 6.10, 9.21, 12.35, 18.77 days

That prints:

73 systems within 20 light-years, the nearest Alpha Centauri
Barnard's Star (バーナード星): 5.98 light-years, M5 V
position from 2MASS, distance from GCTP, Oph
TRAPPIST-1: 7 planets, periods 1.51, 2.42, 4.05, 6.10, 9.21, 12.35, 18.77 days

The stars within 20 light-years

nearStars({ maxLightYears }) gives the systems, nearest first. nearStarByName(text) finds one by its name, its Japanese name, its designation or the name of any of its stars, ignoring case and spacing: Proxima Centauri, Rigil Kentaurus, Sirius B, GJ 699, ウォルフ359.

A system is one star or a group, and its values are those of its primary star (the brightest, or the one the table names). A system with companions lists them in members, the primary first: Alpha Centauri has Rigil Kentaurus, Toliman and Proxima Centauri, each with its own place and distance. starsAtLeast says how many stars the system has, as published for the well-known multiples (3 for Alpha Centauri, 2 for Sirius and 61 Cygni), and is 1 for a star with no known companion. A companion that the two Yale tables do not hold (Sirius B, Procyon B, the brown dwarfs of Epsilon Indi) is a member with a spectral type and a note but no place or distance of its own, and source: "typed".

Each NearStar has:

• id, name, nameJa, designation, aliases and constellation (Cen).
• rightAscension and declination in degrees at J2000, with positionErrorArcsec where it is known.
• parallaxMas and parallaxErrorMas, and the distance lightYears with its lightYearsError. Every system's distance is known to 10% or better, and NEAR_STAR_LIMIT_LY (20) is the limit.
• spectralType and luminosityClass (V for a dwarf), magnitude (V), and the proper motion properMotionRaMas and properMotionDecMas.
• members, starsAtLeast and flags (coarsePosition: the position is the Yale catalogue's own, good to arc-seconds at best; ambiguousMatch: the match to the source is not clear).
• sources: where each value comes from, as one of BSC (the Yale Bright Star Catalogue), GCTP (the Yale General Catalogue of Trigonometric Stellar Parallaxes), 2MASS (the Two Micron All Sky Survey) or typed (a published value typed into the package). The distance is GCTP, BSC or dynamical (from the orbit of a binary).

What is not in it. The list holds the stars that two sources this package can pass on give a distance to: it is the nearest stars as they were measured by 1995, with modern positions. A star found since and not in those tables (Teegarden's Star, GJ 1061, Luhman 16, WISE 0855) is not in the list, because the catalogues that hold its distance are the ESA ones (Hipparcos, Tycho and Gaia), whose non-commercial licence an MIT package cannot pass on. The distances are therefore a little rougher than the modern ones (Proxima is 4.24 light-years here, 4.25 in the literature; Barnard's Star 5.98 and 5.96) and every error is stated. A stated error is the catalogue's formal one, and a Yale-era parallax can be off by more: 51 Pegasi (Helvetios, a host below) is 56.7 light-years here and about 51 in the literature, a difference of about 11%.

The 20 light-year limit is applied to the Yale value, so a star the Yale tables put just beyond it is out although it is nearer in the literature: 82 Eridani, with its planets, is 20.4 light-years here (about 19.7 in the literature). Wolf 1055 (GJ 752 A, HD 180617, 19.1 light-years) is in.

Do not draw the coarse ones as precise. Eight systems have flags.coarsePosition (Lalande 21185, Struve 2398, L 1159-16, G 208-044, L 145-141, CI 20-1046, G 175-034A and L 205-128): their position is the Yale catalogue's own, carried from 1900 to 2000, and is good to arc-seconds at best and to over two arc-minutes at worst (positionErrorArcsec). Draw them as a mark with a margin, not as a point you would aim at, and use the other 65 where a place has to be exact.

The stars with planets

exoplanetHosts({ maxLightYears, minPlanets }) gives the hosts, nearest first, and exoplanetHostByName(text) finds one by its name, its Japanese name, the NASA Exoplanet Archive's name for it (eps Eri) or the name of one of its planets (TRAPPIST-1 e).

How the hosts were picked. A host is in if its distance is known to 10% or better and it is one of these:

• within 50 light-years (EXOPLANET_HOST_LIMIT_LY, 75 hosts), the nearest first, from Proxima Centauri at 4.2 to a G dwarf at 49;
• a star with an IAU proper name beyond that (4 hosts: Errai, Helvetios, Titawin and Hamal);
• TRAPPIST-1, the star with seven Earth-sized planets, whose distance is typed from its discovery papers.

Each ExoplanetHost has name, nameJa, designation (with Greek letters, ε Eri, the same as in /near-stars), archiveName (the Archive's eps Eri), aliases (other spellings that find the host, such as ヘルヴェティオス), constellation, rightAscension, declination, lightYears with lightYearsError, spectralType, magnitude, selection (near, named or typed), nearStarId (the id of its system in /near-stars where it is within 20 light-years), planetCount, planets and sources. Each planet has name, letter, periodDays, periodReference (the paper the period is from), discoveryYear and discoveryMethod. 134 confirmed planets are in all; a planet whose confirmation the literature disputes is left out.

Where the values come from. The planets are the NASA Exoplanet Archive's, and a page that shows them shows EXOPLANET_ARCHIVE_ACKNOWLEDGEMENT, the sentence the Archive asks for. The star's place, distance, spectral type and magnitude are not the Archive's: the Archive's position and distance columns are taken from the TESS Input Catalog, which is built on Gaia, and from Hipparcos, whose licence is non-commercial. They come from the same two Yale tables and 2MASS as the near stars, with a source on each value. A host those tables do not hold, such as LHS 1140, is left out until a source this package can pass on gives its distance. NOTICE.md has the sentence relied on for each source.