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Apus
Constellation
Apus
List of stars in Apus
AbbreviationAps
GenitiveApodis
Pronunciation/ˈeɪpəs/, genitive /ˈeɪpə, ˈæpə, əˈpoʊ-dɪs/[1]
SymbolismThe Bird-of-Paradise[2]
Right ascension13h 51m 07.5441s – 18h 27m 27.8395s[3]
Declination−67.4800797° to −83.1200714°[3]
Area206 sq. deg. (67th)
Main stars4
Bayer/Flamsteed
stars		12
Stars brighter than 3.00m0
Stars within 10.00 pc (32.62 ly)0
Brightest starα Aps (3.83m)
Nearest starHD 128400
Messier objects0
Meteor showers0
Bordering
constellations		Triangulum Australe
Circinus
Musca
Chamaeleon
Octans
Pavo
Ara
Visible at latitudes between +5° and −90°.
Best visible at 21:00 (9 p.m.) during the month of July.

Apus is a small constellation in the southern sky. It represents a bird-of-paradise, and its name means "without feet" in Greek because the bird-of-paradise was once wrongly believed to lack feet. First depicted on a celestial globe by Petrus Plancius in 1598, it was charted on a star atlas by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted and gave the brighter stars their Bayer designations in 1756.

The five brightest stars are all reddish in hue. Shading the others at apparent magnitude 3.8 is Alpha Apodis, an orange giant that has around 48 times the diameter and 928 times the luminosity of the Sun. Marginally fainter is Gamma Apodis, another aging giant star. Delta Apodis is a double star, the two components of which are 103 arcseconds apart and visible with the naked eye. Two star systems have been found to have planets.

History

[edit]
A black line drawing on faded brownish paper depicting a stylized bird with no feet and a triangle superimposed on some stars
Detail of Johann Bayer's 1603 Uranometria, showing the constellations Apus, Chamaeleon, Musca (as "Apis", the Bee), and Triangulum Australe, as well as the South celestial pole.

Apus was one of twelve constellations published by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman who had sailed on the first Dutch trading expedition, known as the Eerste Schipvaart, to the East Indies. It first appeared on a 35-cm (14 in) diameter celestial globe published in 1598 in Amsterdam by Plancius with Jodocus Hondius.[4] De Houtman included it in his southern star catalogue in 1603 under the Dutch name De Paradijs Voghel, "The Bird of Paradise",[5][6] and Plancius called the constellation Paradysvogel Apis Indica; the first word is Dutch for "bird of paradise". Apis (Latin for "bee") is assumed to have been a typographical error for avis ("bird").[5][2]

After its introduction on Plancius's globe, the constellation's first known appearance in a celestial atlas was in German cartographer Johann Bayer's Uranometria of 1603.[4] Bayer called it Apis Indica while fellow astronomers Johannes Kepler and his son-in-law Jakob Bartsch called it Apus or Avis Indica.[7] The name Apus is derived from the Greek apous, meaning "without feet". This referred to the Western misconception that the bird-of-paradise had no feet, which arose because the only specimens available in the West had their feet and wings removed. Such specimens began to arrive in Europe in 1522, when the survivors of Ferdinand Magellan's expedition brought them home.[2] The constellation later lost some of its tail when Nicolas-Louis de Lacaille used those stars to establish Octans in the 1750s.[2]

Characteristics

[edit]

Covering 206.3 square degrees and hence 0.5002% of the sky, Apus ranks 67th of the 88 modern constellations by area.[8] Its position in the Southern Celestial Hemisphere means that the whole constellation is visible to observers south of 7°N.[8][a] It is bordered by Ara, Triangulum Australe and Circinus to the north, Musca and Chamaeleon to the west, Octans to the south, and Pavo to the east. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is "Aps".[9] The official constellation boundaries, as set by Belgian astronomer Eugène Delporte in 1930,[b] are defined by a polygon of six segments (illustrated in infobox). In the equatorial coordinate system, the right ascension coordinates of these borders lie between 13h 49.5m and 18h 27.3m , while the declination coordinates are between −67.48° and −83.12°.[3]

Features

[edit]

Stars

[edit]
See also: List of stars in Apus

Lacaille gave twelve stars Bayer designations, labelling them Alpha through to Kappa, including two stars next to each other as Delta and another two stars near each other as Kappa.[7] Within the constellation's borders, there are 39 stars brighter than or equal to apparent magnitude 6.5.[c][8] Beta, Gamma and Delta Apodis form a narrow triangle, with Alpha Apodis lying to the east.[12] The five brightest stars are all red-tinged, which is unusual among constellations.[13]

Alpha Apodis is an orange giant of spectral type K3III located 430 ± 20 light-years away from Earth,[14] with an apparent magnitude of 3.8.[15] It spent much of its life as a blue-white (B-type) main sequence star before expanding, cooling and brightening as it used up its core hydrogen.[16] It has swollen to 48 times the Sun's diameter,[17] and shines with a luminosity approximately 928 times that of the Sun, with a surface temperature of 4312 K.[18] Beta Apodis is an orange giant 149 ± 2 light-years away,[14] with a magnitude of 4.2.[15] It is around 1.84 times as massive as the Sun, with a surface temperature of 4677 K.[19] Gamma Apodis is a yellow giant of spectral type G8III located 150 ± 4 light-years away,[14] with a magnitude of 3.87. It is approximately 63 times as luminous the Sun, with a surface temperature of 5279 K.[18] Delta Apodis is a double star, the two components of which are 103 arcseconds apart and visible through binoculars.[20] Delta1 is a red giant star of spectral type M4III located 630 ± 30 light-years away.[14] It is a semiregular variable that varies from magnitude +4.66 to +4.87,[21] with pulsations of multiple periods of 68.0, 94.9 and 101.7 days.[22] Delta2 is an orange giant star of spectral type K3III,[23] located 550 ± 10 light-years away,[14] with a magnitude of 5.3. The separate components can be resolved with the naked eye.[15]

The fifth-brightest star is Zeta Apodis at magnitude 4.8,[13] a star that has swollen and cooled to become an orange giant of spectral type K1III, with a surface temperature of 4649 K and a luminosity 133 times that of the Sun.[18] It is 300 ± 4 light-years distant.[14] Near Zeta is Iota Apodis, a binary star system 1,040 ± 60 light-years distant,[14] that is composed of two blue-white main sequence stars that orbit each other every 59.32 years. Of spectral types B9V and B9.5 V, they are both over three times as massive as the Sun.[24]

Eta Apodis is a white main sequence star located 140.8 ± 0.9 light-years distant.[14] Of apparent magnitude 4.89, it is 1.77 times as massive, 15.5 times as luminous as the Sun and has 2.13 times its radius. Aged 250 ± 200 million years old, this star is emitting an excess of 24 μm infrared radiation, which may be caused by a debris disk of dust orbiting at a distance of more than 31 astronomical units from it.[25]

Theta Apodis is a cool red giant of spectral type M7 III located 350 ± 30 light-years distant.[14] It shines with a luminosity approximately 3879 times that of the Sun and has a surface temperature of 3151 K.[18] A semiregular variable, it varies by 0.56 magnitudes with a period of 119 days[26]—or approximately 4 months.[15] It is losing mass at the rate of 1.1 × 10−7 times the mass of the Sun per year through its stellar wind. Dusty material ejected from this star is interacting with the surrounding interstellar medium, forming a bow shock as the star moves through the galaxy.[27] NO Apodis is a red giant of spectral type M3III that varies between magnitudes 5.71 and 5.95.[28] Located 780 ± 20 light-years distant, it shines with a luminosity estimated at 2059 times that of the Sun and has a surface temperature of 3568 K.[18] S Apodis is a rare R Coronae Borealis variable, an extremely hydrogen-deficient supergiant thought to have arisen as the result of the merger of two white dwarfs; fewer than 100 have been discovered as of 2012. It has a baseline magnitude of 9.7.[29] R Apodis is a star that was given a variable star designation, yet has turned out not to be variable. Of magnitude 5.3,[13] it is another orange giant.

Two star systems have had exoplanets discovered by doppler spectroscopy, and the substellar companion of a third star system—the sunlike star HD 131664—has since been found to be a brown dwarf with a calculated mass of the companion to 23 times that of Jupiter (minimum of 18 and maximum of 49 Jovian masses).[30] HD 134606 is a yellow sunlike star of spectral type G6IV that has begun expanding and cooling off the main sequence.[31] Three planets orbit it with periods of 12, 59.5 and 459 days, successively larger as they are further away from the star.[32] HD 137388 is another star—of spectral type K2IV—that is cooler than the Sun and has begun cooling off the main sequence.[31] Around 47% as luminous and 88% as massive as the Sun, with 85% of its diameter, it is thought to be around 7.4 ± 3.9 billion years old.[33] It has a planet that is 79 times as massive as the Earth and orbits its sun every 330 days at an average distance of 0.89 astronomical units (AU).[34]

Deep-sky objects

[edit]
A spherical shaped group of a multitude of stars
Globular cluster IC 4499 taken by Hubble Space Telescope.[35]

The Milky Way covers much of the constellation's area.[36] Of the deep-sky objects in Apus, there are two prominent globular clusters—NGC 6101 and IC 4499—and a large faint nebula that covers several degrees east of Beta and Gamma Apodis.[37] NGC 6101 is a globular cluster of apparent magnitude 9.2 located around 50,000 light-years distant from Earth,[38] which is around 160 light-years across. Around 13 billion years old, it contains a high concentration of massive bright stars known as blue stragglers, thought to be the result of two stars merging.[39] IC 4499 is a loose globular cluster in the medium-far galactic halo;[40] its apparent magnitude is 10.6.[41]

The galaxies in the constellation are faint.[37] IC 4633 is a very faint spiral galaxy surrounded by a vast amount of Milky Way line-of-sight integrated flux nebulae—large faint clouds thought to be lit by large numbers of stars.[38]

See also

[edit]

Notes

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Apus

View on Grokipedia
from Grokipedia
Apus is a small southern constellation representing the , named from the Greek word apous meaning "without feet," a reference to early European specimens of the bird that arrived without legs or wings due to preparation methods. It spans 206 square degrees in the sky, ranking as the 67th largest constellation, and is visible from latitudes between +5° and -90°, with optimal viewing in . Introduced in the late by Dutch navigators and during expeditions to the , Apus was first depicted on a celestial globe by in 1598 as Paradys-vogel Apis Indica, later standardized as Apus by in 1627. The constellation has no ancient mythological associations, as its stars were unknown to observers before the Age of Discovery, and it was created to fill gaps in southern sky charts. In the 1750s, French astronomer Nicolas-Louis de Lacaille adjusted its boundaries, shortening its "tail" to accommodate the new constellation near the south . Apus lies within 7 degrees of the south celestial pole, bordered by the constellations Ara, Pavo, , , , Musca, and , with right ascension ranging from 13h 49.5m to 18h 27.3m and declination from -83.12° to -67.48°. It is relatively faint, with its brightest star, Alpha Apodis (also known as Paradys), an orange giant of apparent magnitude 3.82 located 430 light-years away. Other notable stars include Beta Apodis, a K-type giant of magnitude 4.24 at 149 light-years, and Gamma Apodis, a G9 III giant of magnitude 3.86 at 150 light-years. The constellation hosts deep-sky objects such as the globular clusters NGC 6101 (magnitude 9.0, 47,600 light-years distant) and IC 4499 (magnitude 9.76, approximately 50,000 light-years away).

History and Nomenclature

Historical Development

The constellation Apus originated in the late 16th century when Dutch-Flemish astronomer and cartographer created it based on star observations recorded by explorers and during their 1595–1597 voyages to the for the . Plancius first depicted Apus on a celestial globe produced in in 1598 in collaboration with engraver , representing the —a species encountered by the explorers and prized for its exotic plumage, with early accounts mistakenly describing it as footless. This marked Apus as one of 12 new southern constellations devised by Plancius to map previously uncharted skies visible only from the . Apus received wider recognition through its inclusion in Johann Bayer's influential star atlas Uranometria in 1603, where Bayer illustrated the figure as a bird without legs or tail, drawing directly from Plancius's design. The name was later standardized as Apus by in his 1627 star atlas to avoid confusion with the bee (Apis). Over a century later, French astronomer Nicolas-Louis de Lacaille refined the constellation during his 1751–1754 expedition to the , where he systematically cataloged nearly 10,000 southern stars; in his 1763 publication Coelum Australe Stelliferum, Lacaille formalized Apus's boundaries and adjusted its figure slightly by separating nearby stars into the new constellation , while depicting it as Apus. Lacaille's work significantly advanced southern sky mapping by introducing precise coordinates and 14 additional constellations to fill gaps in the existing framework. Unlike ancient constellations rooted in , Apus has no such traditional basis and represents a modern invention from the Age of Exploration, reflecting European encounters with exotic fauna from the . In 1922, the (IAU) officially adopted Apus as one of the 88 standardized constellations, defining its precise boundaries to cover the entire without overlap, thus cementing the contributions of Plancius, , and Lacaille in establishing a comprehensive southern .

Naming Conventions

The name Apus is derived from the Greek word apous, meaning "footless," a reference to the bird of paradise (Aves paradisi), which early European explorers depicted without feet in illustrations due to the removal of legs from imported specimens during preparation. The genitive form of the constellation's name is Apodis. Petrus Plancius first charted Apus on his 1598 celestial globe, naming it after the exotic bird known to Dutch traders. The (IAU) officially adopted the three-letter abbreviation "Aps" for Apus as part of its standardization of constellation nomenclature in 1922. Within Apus, individual stars are primarily identified using Bayer designations, a system in which Greek letters followed by the genitive Apodis denote relative brightness, as assigned by French astronomer Nicolas Louis de Lacaille during his observations at the and first published in his 1756 preliminary catalog of southern stars. For example, α Apodis (Alpha Apodis) marks the constellation's brightest star at magnitude 3.8. Lacaille also introduced a Flamsteed-style numbering system in his catalog, assigning sequential numbers to southern stars, including those in Apus, to supplement the letter designations for fainter objects. In traditional Chinese astronomy, the stars of Apus correspond to the asterism E Cho (or I Ch'o), interpreted as the Curious Sparrow, and sometimes as the Little Wonder Bird, though the modern IAU-aligned name is 天燕座 (Tiān Yàn Zuò), the Celestial Swallow constellation.

Observational Characteristics

Visibility and Seasons

Apus is best observed from locations in the Southern Hemisphere south of 5° N latitude, where it can be seen low on the southern horizon or higher depending on the observer's position, and it remains invisible from most northern temperate regions. For observers in far southern latitudes, particularly south of 23° S, the constellation is circumpolar, circling the without setting and remaining visible throughout the year under clear conditions. It culminates at midnight around late May for northern observers near the who can glimpse it, providing the highest elevation during that period. In mid-southern latitudes, such as around 35° S, Apus appears prominently in the evening sky from through , coinciding with the Southern Hemisphere's autumn and winter seasons when longer nights aid observation. The constellation spans right ascensions from approximately 14 h to 18 h and declinations from -83° to -68°, positioning it near the south and making it a fixture of the austral sky during these months. Optimal viewing occurs around 9 p.m. in , when it reaches its highest point for evening stargazers in these regions. Due to its faint nature, with all stars dimmer than magnitude 3.8, Apus demands dark, rural skies free from for effective naked-eye viewing, as urban glow can render it nearly invisible. are often necessary to resolve its stellar pattern against the background, especially for beginners, and even then, patience is required under suboptimal conditions like moonlight or atmospheric haze. The constellation covers an area of 206 square degrees, ranking 67th in size among modern constellations. The constellation's stars were meticulously surveyed during French astronomer Nicolas-Louis de Lacaille's expedition to the from 1751 to 1752, where he established an and cataloged nearly 10,000 southern stars, contributing foundational data for mapping faint southern patterns like Apus. Lacaille's observations from this site, at approximately 34° S latitude, provided key positions that informed his 1763 celestial atlas, in which he cataloged the stars of the constellation.

Size and Position

Apus encompasses an area of 206 square degrees on the , making it the 67th largest of the 88 modern constellations recognized by the (IAU). The boundaries of Apus were formally delimited in 1930 by Belgian astronomer Eugène Delporte under the auspices of the IAU, using arcs of and to create precise, non-overlapping regions covering the entire sky. In equatorial coordinates, Apus spans from 13h 51m to 18h 27m and -67.5° to -83.1°, positioning it firmly in the and placing its southern limit just 7° from the south celestial pole. This proximity to the pole renders Apus for observers south of 23° S, though its faint stars pose challenges in visibility from urban areas affected by . Apus borders the constellations Ara to the north, Triangulum Australe to the northeast, to the east, Musca to the southeast, to the south, to the southwest, and Pavo to the west, forming a compact region near the southern plane of the . Its location far from the —well south of the zodiacal band—means it contains no significant overlap with the paths of the Sun, , or planets as seen from .

Stellar Features

Principal Stars

Alpha Apodis (α Aps) is the brightest star in the constellation, exhibiting an apparent visual magnitude of 3.80 and classified as an orange giant of type K3 III with mild carbon-nitrogen peculiarities. Located at a distance of approximately 498 light-years based on Data Release 3 measurements of 6.551 ± 0.113 mas, it represents an evolved star in the giant phase, having depleted its core hydrogen and expanded significantly. The star displays proper motions of -5.13 mas/yr in and -16.30 mas/yr in , along with a of -0.10 ± 0.7 km/s, indicating relatively slow space motion relative to the Sun. The Bayer-designated second star, Beta Apodis (β Aps), has an apparent visual magnitude of 4.24 and is a yellow-orange giant of type K0 III. DR3 data place it at a distance of about 156 light-years, derived from a of 20.954 ± 0.160 mas, making it one of the closer principal stars in Apus. Its high proper motions of -281.99 mas/yr in and -354.84 mas/yr in , combined with a of -30.02 ± 0.16 km/s, highlight its significant transverse motion across the sky, approaching the solar system. Compared to Alpha Apodis, Beta Apodis is intrinsically less luminous but appears brighter due to its proximity. Gamma Apodis (γ Aps) ranks as the second brightest star in the constellation with an apparent visual magnitude of 3.85, identified as a yellow giant of spectral type III. At a distance of roughly 153 light-years from DR3 parallax of 21.303 ± 0.152 mas, it is similar in proximity to Beta Apodis. The star exhibits proper motions of -125.58 mas/yr in and -78.21 mas/yr in , with a radial velocity of 5.40 ± 0.7 km/s, suggesting mild recession from the Sun. As a giant, it has evolved off the and contributes to the constellation's overall reddish hue among its brighter members.
StarBayerV MagnitudeSpectral TypeDistance (ly)pmRA (mas/yr)pmDec (mas/yr)Radial Velocity (km/s)
Alpha Apodisα Aps3.80K3 III498-5.13-16.30-0.10
Beta Apodisβ Aps4.24K0 III156-282.0-354.8-30.02
Gamma Apodisγ Aps3.85G8 III153-125.6-78.215.40
Other notable principal stars include Epsilon Apodis (ε Aps), a blue main-sequence star of spectral type B3 V with an of 5.05, situated 535 light-years away per Gaia DR3 parallax data. It shows proper motions of -8.76 mas/yr in and -15.00 mas/yr in , and a of 4.50 km/s. Zeta Apodis (ζ Aps), an orange giant of type III at magnitude 4.78, lies approximately 293 light-years distant, with proper motions of -37.44 mas/yr and -7.93 mas/yr, and a of 11.36 km/s. The sequence of Bayer designations from Alpha to Zeta outlines the faint, bird-like pattern of Apus, with these principal stars marking the head, body, and tail of the celestial , though the constellation's overall dimness limits its visibility to southern latitudes. Updated measurements from the and missions provide precise distances and motions, refining our understanding of these stars' positions within the .

Variable and Multiple Stars

Apus contains a number of variable and multiple star systems that exhibit dynamic behaviors useful for studying stellar pulsations, binary interactions, and evolutionary stages. Among the brighter variables is Epsilon Apodis, a Gamma Cassiopeiae-type variable with small-amplitude irregularities varying from magnitude 4.99 to 5.04 due to shell ejections in its envelope. A notable irregular variable is S Apodis, an R Coronae Borealis-type that undergoes sudden brightness declines caused by carbon dust formation obscuring the hydrogen-deficient ; it normally shines at magnitude ~9.8 but can fade to 14 or fainter irregularly, with no fixed period. Multiple star systems in Apus include hierarchical configurations that reveal orbital dynamics over long baselines. Iota Apodis is a with a combined apparent magnitude of 5.39, consisting of two B9 V stars orbiting each other with a period of approximately 1350 days. Post-2020 data from the mission have revealed new binaries and variables in Apus, including low-mass eclipsing pairs suitable for transit searches due to their precise light curves and parallaxes. These discoveries, part of Gaia's catalog of over 10 million variables, enhance understanding of short-period systems in southern skies. Observational techniques for confirming variability in Apus stars rely on time-series photometry, where repeated measurements in filters like V-band track magnitude changes to determine amplitudes (peak-to-trough differences) and periods (via of light curves). Small telescopes equipped with CCDs achieve the necessary precision for detecting variations as low as 0.01 magnitudes, facilitating period confirmation through phase folding.

Deep-Sky Objects

Globular Clusters

NGC 6101, also known as Caldwell 107, is the principal in the constellation Apus, located approximately 47,600 light-years from and about 36,500 light-years from the . This metal-poor cluster ([Fe/H] = –1.76 dex) has an estimated age of 12.54 billion years, making it one of the older stellar aggregates in the , comparable to many ancient globulars formed in the early . With an apparent visual magnitude of 9.0 and an angular diameter of 10.7 arcminutes, it spans a physical size of roughly 160 light-years across. Its integrated spectral type is classified as F8, reflecting the collective light from its predominantly low-metallicity, evolved stars. Structurally, NGC 6101 belongs to Shapley-Sawyer Concentration Class X, indicating a loosely concentrated form with a sparse core and irregular distribution of , where individual members are resolvable only in telescopes of 20 cm or larger. Dynamical studies, including imaging, reveal a lack of significant mass segregation among its stellar , suggesting a relatively relaxed evolutionary state with minimal central cusp formation. This configuration implies that heavier , such as potential compact remnants, have not dynamically dominated the core, consistent with models of low-mass globular clusters experiencing moderate tidal influences from the Galaxy. Dynamical studies using N-body simulations suggest a retained of stellar-mass black holes (>50% retention fraction) that could explain the lack of significant mass segregation among visible and influence the cluster's long-term dynamics. Discovered on June 1, 1826, by Scottish astronomer James Dunlop using a 9-inch reflector, NGC 6101 was cataloged as Dunlop 68 and later included in John Herschel's observations during the 1830s, where it was noted as a faint, large nebulous object. Its southern location (declination –72°) prevented inclusion in Charles Messier's northern-hemisphere catalog from the 18th century, which focused on objects visible from Europe. Positioned in the northern part of Apus near the border with Triangulum Australe, about 4° southwest of Alpha Trianguli Australis, the cluster is best observed from mid-southern latitudes during late spring and summer in the Southern Hemisphere. It appears as a fuzzy patch in small amateur telescopes (e.g., 80 mm aperture binoculars suffice for detection), but reveals sparse stellar resolution and subtle asymmetries in larger instruments under dark skies. Hubble observations have further highlighted its star density profiles, underscoring its role in probing the formation and retention of compact objects in metal-poor environments. Another in Apus is IC 4499, a loose cluster (Shapley-Sawyer class XI) with an of 9.8 and an angular diameter of 7.6 arcminutes. Located approximately 50,000 light-years away in the , it was discovered by in 1834 and lies close to the south celestial pole.

Galaxies and Nebulae

Apus contains several faint galaxies and one notable , though it lacks prominent emission nebulae or large-scale gaseous structures visible to amateur observers. The most prominent galaxy is IC 4633, a classified as type Sc with an of 12.4. Located approximately 100 million light-years away, it exhibits a of z = 0.0099, corresponding to a of about 2953 km/s. IC 4633 is rich in star-forming regions and hosts an , categorizing it as a Type 2 where the nucleus's light is partially obscured by dust, contributing to its emission-line spectrum. imaging reveals its spiral structure partially veiled by foreground dust from the South Celestial Serpent cloud, highlighting bright star-forming knots along its arms. No confirmed barred morphology (SBc) is detailed in primary observations, though its core shows asymmetry consistent with nuclear activity. Another notable extragalactic object is ESO 44-3 (alternative designation for IC 4633), emphasizing its Seyfert characteristics with an around 12-13 in optical bands and a distance aligning with the 100 million estimate from Hubble flow models. The active nucleus drives ionized gas outflows, detectable in emission lines, though detailed confirms no extreme variability typical of brighter Seyferts. The constellation's primary nebula is the Hen 2-131 (also known as He 2-131), with an apparent V magnitude of 10.5. Situated about 7,200 light-years away, it surrounds the central star HD 138403, a weak-emission-line star with V magnitude approximately 15.9. The nebula's compact structure, spanning roughly 20 arcseconds, suggests a dynamical age of around 10,000 years based on its expansion velocity of 11.5 km/s and ionized shell radius. Recent astronomical research, including 2024 Hubble observations, has refined the structure of IC 4633, revealing enhanced rates amid its obscured disk. Apus shows no major nebulae, but diffuse emission regions associated with integrated flux nebulae near the plane overlay foreground views of IC 4633. These objects are cataloged in the Index Catalogue (IC) for galaxies like IC 4633 and the Perek-Kohoutek (PK) system for planetary nebulae such as Hen 2-131, with coordinates aligned to Apus boundaries (RA 13h 51m to 18h 27m, Dec -83° to -67°). While the Herschel 400 and Caldwell catalogs include Apus objects, they primarily feature globular clusters rather than galaxies or nebulae in this region.

References

  1. http://www.ianridpath.com/startales/apus.html
  2. https://www.constellation-guide.com/constellation-list/apus-constellation/
  3. https://noirlab.edu/public/education/constellations/apus/
  4. http://www.ianridpath.com/startales/plancius-globe.html
  5. https://www.lindahall.org/about/news/scientist-of-the-day/petrus-plancius/
  6. https://www.universetoday.com/articles/apus
  7. https://phys.org/news/2016-02-apus-constellation.html
  8. http://www.ianridpath.com/iaulist1.html
  9. https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Apus*.html
  10. https://astro4edu.org/resources/diagram/Df427a55Gc18/
  11. https://www.deepskycorner.ch/con/apus.en.php
  12. https://www.seasky.org/constellations/constellation-apus.html
  13. https://www.go-astronomy.com/constellations.php?Name=Apus
  14. https://theplanets.org/constellations/apus-constellation/
  15. https://simbad.u-strasbg.fr/simbad/sim-id?Ident=Alpha+Apodis
  16. https://simbad.u-strasbg.fr/simbad/sim-id?Ident=Beta+Apodis
  17. https://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+Apodis
  18. https://simbad.u-strasbg.fr/simbad/sim-id?Ident=Epsilon+Apodis
  19. https://simbad.u-strasbg.fr/simbad/sim-id?Ident=Zeta+Apodis
  20. https://www.universeguide.com/star/70248/epsilonapodis
  21. https://academic.oup.com/mnras/article/302/2/341/968786
  22. https://www.aanda.org/articles/aa/full_html/2023/06/aa44242-22/aa44242-22.html
  23. https://academic.oup.com/mnras/article/519/4/5271/6961770
  24. https://astro4dev.org/wp-content/uploads/2013/09/Variable_stars.pdf
  25. https://www.constellation-guide.com/globular-cluster-ngc-6101-in-apus/
  26. https://academic.oup.com/mnras/article/462/3/2333/2589390
  27. https://ui.adsabs.harvard.edu/abs/2015ApJ...810...40D/abstract
  28. https://www.deepskycorner.ch/obj/ngc6101.en.php
  29. http://www.messier.seds.org/xtra/history/lac-cat.html
  30. https://theskylive.com/sky/deepsky/ngc6101-object
  31. https://science.nasa.gov/image-detail/ngc6101_wfc3_acs_21pi_cropfinal/
  32. https://simbad.cds.unistra.fr/simbad/sim-basic?Ident=IC+4633
  33. https://science.nasa.gov/missions/hubble/hubble-spots-a-galaxy-hidden-in-a-dark-cloud/
  34. https://esahubble.org/images/potw2415a/
  35. http://ui.adsabs.harvard.edu/abs/1993A&A...267L...8H/abstract
  36. https://www.deepskycorner.ch/obj/ic4633.en.php
  37. https://in-the-sky.org/data/object.php?id=PK329%2B02.1
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