DOCSLIB.ORG

Characterising the Magnetic Fields of Nearby Molecular Clouds Using Submillimeter Polarization Observations

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Characterising the Magnetic Fields of Nearby Molecular Clouds Using Submillimeter Polarization Observations MNRAS 000,1–17 (0000) Preprint 13 April 2021 Compiled using MNRAS LATEX style file v3.0 Characterising the Magnetic Fields of Nearby Molecular Clouds using Submillimeter Polarization Observations Colin H Sullivan,1,2¢ L. M. Fissel,2,3 P. K. King,1,4,5 C.-Y. Chen,1,4 Z.-Y. Li,1 and J. D. Soler6 1Department of Astronomy, University of Virginia, Charlottesville VA, 22904 2National Radio Astronomy Observatory, Charlottesville, VA, 22904 3Department of Physics, Engineering Physics, and Astronomy, Queen’s University, Kingston, ON, Canada, K7L 3N6 4Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723 5Lawrence Livermore National Laboratory, Livermore, 7000 East Ave, Livermore, CA 94550, USA 6Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany Accepted 2021 February 23. Received 2021 February 21; in original form 2019 October 30 ABSTRACT Of all the factors that influence star formation, magnetic fields are perhaps the least well understood. The goal of this paper is to characterize the 3D magnetic field properties of nearby molecular clouds through various methods of statistically analyzing maps of polarized dust emission. Our study focuses on nine clouds, with data taken from the Planck Sky Survey as well as data from the BLASTPol observations of Vela C. We compare the distributions of polarization fraction (p), dispersion in polarization angles (S), and hydrogen column density (#H) for each of our targeted clouds. To broaden the scope of our analysis, we compare the distributions of our clouds’ polarization observables with measurements from synthetic polarization maps generated from numerical simulations. We also use the distribution of polarization fraction measurements to estimate the inclination angle of each cloud’s cloud- scale magnetic field. We obtain a range of inclination angles associated with our clouds, ◦ ◦ varying from 16 to 69 . We establish inverse correlations between ? and both S and #H in almost every cloud, but we are unable to establish a statistically robust S vs #H trend. By comparing the results of these different statistical analysis techniques, we are able to propose a more comprehensive view of each cloud’s 3D magnetic field properties. These detailed cloud analyses will be useful in the continued studies of cloud-scale magnetic fields and the ways in which they affect star formation within these molecular clouds. Key words: Polarization – Magnetic Fields – ISM: Clouds 1 INTRODUCTION difficult. The long observation times required also make Zeeman observations impractical for producing cloud-scale maps. Molecular Clouds (MCs) are the birthplaces of stars. These clouds are typically cold (10-30K) and have dense sub-regions within them As an alternative, linearly polarized thermal dust emission is that may collapse under gravity to form stars. The evolution and commonly used to create large-scale maps to study MC-scale mag- arXiv:2104.04673v1 [astro-ph.GA] 10 Apr 2021 efficiency of star formation within MCs are regulated by a number of netic fields. This technique relies heavily on the orientation of their factors, primarily gravity, turbulence, and magnetic fields (McKee dust grains, as dust grains tend to align with their minor axes ori- & Ostriker 2007). Among these physical processes, magnetic fields ented parallel to the local magnetic field lines. This alignment is are perhaps the least well understood, and this is largely because most likely caused by radiative torques from the local radiation magnetic fields are very difficult to observe directly. Although the field (see Andersson et al. 2015 for a review). This process cre- line-of-sight component of a magnetic field can be measured by ates a net linear polarization orientation of the emitted light that is Zeeman spectral line splitting (Crutcher 2012), the width of the perpendicular to the magnetic field direction projected on the sky. line splitting is typically much less than the thermally broadened By measuring linear polarization of the sub-mm radiation emit- line width, which makes detection of Zeeman splitting extremely ted by dust grains within the molecular cloud and rotating the polar- ization orientation by 90◦, we can map the corresponding magnetic field orientation projected on the plane of sky. These measured ori- entation values represent the averaged magnetic field orientation ¢ E-mail: [email protected] within the volume of the cloud probed by the telescope beam, and © 0000 The Authors 2 C. Sullivan et al. are most sensitive to regions of high dust emissivity and efficient generated using the Athena MHD code (Chen et al. 2016), with the grain alignment. goal of reproducing the correlations between ?, #H, and S found In addition to the inferred plane-of-sky magnetic field orienta- in observations of the Vela C GMC in Fissel et al.(2016). In order tion, there are several other polarization parameters that can be used to reproduce the high levels of S, large range of ?, and the level to study the structure and geometry of magnetic fields in molecular of anti-correlation between ? and S, the authors speculated that clouds. The polarization fraction (?) of the emission is the frac- Vela C must have either a weak magnetic field or a stronger field tion of observed radiation that is linearly polarized. ? is sensitive that is highly inclined with respect to the plane of the sky. Other to the efficiency with which grains are aligned with respect to the studies analyzing the orientation of cloud structure with respect to magnetic field, the degree of disorder in the plane-of-sky magnetic the magnetic field (Soler et al. 2017, Fissel et al. 2019) have sug- field within the dust column probed by the polarimeter, and the gested that Vela C has a reasonably strong cloud-scale magnetic inclination angle of the cloud’s magnetic field with respect to the field, and so it seems more likely that Vela C’s magnetic field must plane of the sky. In addition, the local polarization angle dispersion be significantly inclined with respect to the plane of the sky (King (S) is used to measure the disorder in the projected magnetic field et al. 2018, Chen et al. 2019). orientation at a given location in the cloud (Fissel et al. 2016). In Here, we extended the comparisons of the ?, #H, and S dis- addition to these polarimetric properties, we also consider the hy- tributions to a larger sample size of molecular clouds by including drogen column density (#H) in our analysis. This quantity is used Planck 353 GHz polarization observations of eight nearby clouds. as a proxy for the total mass surface density of our clouds, and is In this way, we will determine if the results of King et al.(2018) thus useful for characterising the gas substructure of MCs. are consistent with a larger sample size of nearby MCs. The eight Lower resolution polarization studies, such as the 1◦ reso- Planck clouds included in this study are all nearby and relatively low 5 lution, all-sky analysis of Planck Collaboration XIX(2015), or the mass, while Vela C is more distant and massive ("Vela ¡ 10 " ). BLASTPol 20.5 resolution study of the Vela C giant molecular cloud Significantly higher resolution (2.50 as opposed to 150 for the Planck (GMC) (Fissel et al. 2016), have identified several correlations be- observations) means that Vela C has a linear resolution almost equal tween p, S, and #H. The first trend is a negative correlation between to the closest of the Planck clouds. Linear resolution and other such p and S: as S increases, p decreases. This trend could be related cloud-specific quantities are listed in Table1. to the differences in the 3D geometry of the magnetic field in dif- In this paper, we use our increased sample size to provide more ferent parts of the cloud as ? is proportional to cos2 W, where W is stringent tests of the analyses presented in King et al.(2018, 2019), the inclination angle of the magnetic field with respect to the plane Chen et al.(2019), Fissel et al.(2019). We also compare our results of the sky (Hildebrand 1988). For cloud sightlines where the mag- to multiple intermediate-results Planck papers, specifically Planck netic field is nearly parallel to the line-of-sight, ? values tend to Collaboration XX et al.(2015), Planck Collaboration XIX(2015) be lower, and upon projection onto the plane-of-sky the angles can and Planck Collaboration et al.(2020). This paper is organized as vary greatly between adjacent sightlines, leading to large values of follows: Section2 - Observations and Data Reduction; Section3 S. - Comparison of polarization properties between different clouds; In addition, a weak, disordered magnetic field provides little Section4 - Comparison with synthetic polarization observations resistance to turbulent motions, and can be easily driven to a highly of 3D MHD simulations reported in King et al.(2018); Section disordered state, which produces large values for S. This in turn 5 - Conclusions. In AppendixA, we discuss how our results are leads to significantly lower p values. Strong magnetic fields are able influenced by different methods selecting cloud sightlines. to resist turbulent motions that are perpendicular to their field lines, and thus tend to have lower values for S. Low p and high S values can therefore indicate a weak/disordered magnetic field and/or a 2 OBSERVATIONS & DATA REDUCTION nearly line-of-sight magnetic field orientation, while high p values and low S values can indicate a strongly ordered magnetic field In this paper, we analyze thermal dust emission polarization obser- and/or a nearly plane-of-sky magnetic field orientation. vations of nine nearby MCs. For eight of the clouds we use 353 GHz The second observed trend that we will investigate is the anti- polarization maps from the Planck satellite, first presented in Planck correlation between polarization fraction ? and hydrogen column Collaboration XXXV(2016).
Load more

Recommended publications
  • MESSIER 13 RA(2000) : 16H 41M 42S DEC(2000): +36° 27'
    MESSIER 13 RA(2000) : 16h 41m 42s DEC(2000): +36° 27’ 41” BASIC INFORMATION OBJECT TYPE: Globular Cluster CONSTELLATION: Hercules BEST VIEW: Late July DISCOVERY: Edmond Halley, 1714 DISTANCE: 25,100 ly DIAMETER: 145 ly APPARENT MAGNITUDE: +5.8 APPARENT DIMENSIONS: 20’ Starry Night FOV: 1.00 Lyra FOV: 60.00 Libra MESSIER 6 (Butterfly Cluster) RA(2000) : 17Ophiuchus h 40m 20s DEC(2000): -32° 15’ 12” M6 Sagitta Serpens Cauda Vulpecula Scutum Scorpius Aquila M6 FOV: 5.00 Telrad Delphinus Norma Sagittarius Corona Australis Ara Equuleus M6 Triangulum Australe BASIC INFORMATION OBJECT TYPE: Open Cluster Telescopium CONSTELLATION: Scorpius Capricornus BEST VIEW: August DISCOVERY: Giovanni Batista Hodierna, c. 1654 DISTANCE: 1600 ly MicroscopiumDIAMETER: 12 – 25 ly Pavo APPARENT MAGNITUDE: +4.2 APPARENT DIMENSIONS: 25’ – 54’ AGE: 50 – 100 million years Telrad Indus MESSIER 7 (Ptolemy’s Cluster) RA(2000) : 17h 53m 51s DEC(2000): -34° 47’ 36” BASIC INFORMATION OBJECT TYPE: Open Cluster CONSTELLATION: Scorpius BEST VIEW: August DISCOVERY: Claudius Ptolemy, 130 A.D. DISTANCE: 900 – 1000 ly DIAMETER: 20 – 25 ly APPARENT MAGNITUDE: +3.3 APPARENT DIMENSIONS: 80’ AGE: ~220 million years FOV:Starry 1.00Night FOV: 60.00 Hercules Libra MESSIER 8 (THE LAGOON NEBULA) RA(2000) : 18h 03m 37s DEC(2000): -24° 23’ 12” Lyra M8 Ophiuchus Serpens Cauda Cygnus Scorpius Sagitta M8 FOV: 5.00 Scutum Telrad Vulpecula Aquila Ara Corona Australis Sagittarius Delphinus M8 BASIC INFORMATION Telescopium OBJECT TYPE: Star Forming Region CONSTELLATION: Sagittarius Equuleus BEST
    [Show full text]
  • 1. What Are the RA and DEC of Perseus Constellation? at What Time
    1. What are the RA and DEC of Perseus constellation? At what time do you expect it to transit at Kharagpur on 23 January? Does the Sun ever visit this constellation? How high in the sky from the horizon, will this constellation appear? 2. Sketch the Orion constellation, and indicate the location of the Orion nebua. What is the Orion nebula? 3. Explain briefly why Earth’s rotation axis precesses. What is the rate of precession? 4. Verify that a(1 − e2) u−1 = r = 1+ e cos φ with a = −2GM/E and e = [1+2J 2E2/G2M 2]1/2 is acually a solution to the equation 2 1 du E = J 2 + J 2u2 − GMu 2 dφ! which governs the trajectory under the gravitational attraction of a massive object. 5. Show that 4π2 P 2 = a3 GM for a general elliptic orbit. 6. Assuming that the Earth has a rotational period of 24 hrs around its own axis and revolution period of 365.25 days around the Sun, what is the length of a Solar day? After what period do distant stars come back to the same position on the sky? 7. Given Comet Halley has period 75 yrs, determine the semimajor axis of its orbit? 8. Consider an orbit around the Sun with e = 0.3. What is the ratio of the speeds at apogee and perigee? 9. At what height from center of Earth do we have geostationary satellite orbits? 10. For a central force motion in a gravitational potential α/r, show that A~ = ~v × L~ + α~r/r is conserved.
    [Show full text]
  • Naming the Extrasolar Planets
    Naming the extrasolar planets W. Lyra Max Planck Institute for Astronomy, K¨onigstuhl 17, 69177, Heidelberg, Germany [email protected] Abstract and OGLE-TR-182 b, which does not help educators convey the message that these planets are quite similar to Jupiter. Extrasolar planets are not named and are referred to only In stark contrast, the sentence“planet Apollo is a gas giant by their assigned scientific designation. The reason given like Jupiter” is heavily - yet invisibly - coated with Coper- by the IAU to not name the planets is that it is consid- nicanism. ered impractical as planets are expected to be common. I One reason given by the IAU for not considering naming advance some reasons as to why this logic is flawed, and sug- the extrasolar planets is that it is a task deemed impractical. gest names for the 403 extrasolar planet candidates known One source is quoted as having said “if planets are found to as of Oct 2009. The names follow a scheme of association occur very frequently in the Universe, a system of individual with the constellation that the host star pertains to, and names for planets might well rapidly be found equally im- therefore are mostly drawn from Roman-Greek mythology. practicable as it is for stars, as planet discoveries progress.” Other mythologies may also be used given that a suitable 1. This leads to a second argument. It is indeed impractical association is established. to name all stars. But some stars are named nonetheless. In fact, all other classes of astronomical bodies are named.
    [Show full text]
  • Wynyard Planetarium & Observatory a Autumn Observing Notes
    Wynyard Planetarium & Observatory A Autumn Observing Notes Wynyard Planetarium & Observatory PUBLIC OBSERVING – Autumn Tour of the Sky with the Naked Eye CASSIOPEIA Look for the ‘W’ 4 shape 3 Polaris URSA MINOR Notice how the constellations swing around Polaris during the night Pherkad Kochab Is Kochab orange compared 2 to Polaris? Pointers Is Dubhe Dubhe yellowish compared to Merak? 1 Merak THE PLOUGH Figure 1: Sketch of the northern sky in autumn. © Rob Peeling, CaDAS, 2007 version 1.2 Wynyard Planetarium & Observatory PUBLIC OBSERVING – Autumn North 1. On leaving the planetarium, turn around and look northwards over the roof of the building. Close to the horizon is a group of stars like the outline of a saucepan with the handle stretching to your left. This is the Plough (also called the Big Dipper) and is part of the constellation Ursa Major, the Great Bear. The two right-hand stars are called the Pointers. Can you tell that the higher of the two, Dubhe is slightly yellowish compared to the lower, Merak? Check with binoculars. Not all stars are white. The colour shows that Dubhe is cooler than Merak in the same way that red-hot is cooler than white- hot. 2. Use the Pointers to guide you upwards to the next bright star. This is Polaris, the Pole (or North) Star. Note that it is not the brightest star in the sky, a common misconception. Below and to the left are two prominent but fainter stars. These are Kochab and Pherkad, the Guardians of the Pole. Look carefully and you will notice that Kochab is slightly orange when compared to Polaris.
    [Show full text]
  • The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens
    The Mid-Infrared Extinction Law in the Ophiuchus, Perseus, and Serpens Molecular Clouds Nicholas L. Chapman1,2, Lee G. Mundy1, Shih-Ping Lai3, Neal J. Evans II4 ABSTRACT We compute the mid-infrared extinction law from 3.6−24µm in three molecu- lar clouds: Ophiuchus, Perseus, and Serpens, by combining data from the “Cores to Disks” Spitzer Legacy Science program with deep JHKs imaging. Using a new technique, we are able to calculate the line-of-sight extinction law towards each background star in our fields. With these line-of-sight measurements, we create, for the first time, maps of the χ2 deviation of the data from two extinc- tion law models. Because our χ2 maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a func- tion of the total column density. In the Spitzer IRAC bands, 3.6 − 8 µm, we see evidence for grain growth. Below AKs =0.5, our extinction law is well-fit by the Weingartner & Draine (2001) RV = 3.1 diffuse interstellar medium dust model. As the extinction increases, our law gradually flattens, and for AKs ≥ 1, the data are more consistent with the Weingartner & Draine RV = 5.5 model that uses larger maximum dust grain sizes. At 24 µm, our extinction law is 2 − 4× higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. (2007). Lastly, from our χ2 maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density.
    [Show full text]
  • The Lore of the Stars, for Amateur Campfire Sages
    obscure. Various claims have been made about Babylonian innovations and the similarity between the Greek zodiac and the stories, dating from the third millennium BCE, of Gilgamesh, a legendary Sumerian hero who encountered animals and characters similar to those of the zodiac. Some of the Babylonian constellations may have been popularized in the Greek world through the conquest of The Lore of the Stars, Alexander in the fourth century BCE. Alexander himself sent captured Babylonian texts back For Amateur Campfire Sages to Greece for his tutor Aristotle to interpret. Even earlier than this, Babylonian astronomy by Anders Hove would have been familiar to the Persians, who July 2002 occupied Greece several centuries before Alexander’s day. Although we may properly credit the Greeks with completing the Babylonian work, it is clear that the Babylonians did develop some of the symbols and constellations later adopted by the Greeks for their zodiac. Contrary to the story of the star-counter in Le Petit Prince, there aren’t unnumerable stars Cuneiform tablets using symbols similar to in the night sky, at least so far as we can see those used later for constellations may have with our own eyes. Only about a thousand are some relationship to astronomy, or they may visible. Almost all have names or Greek letter not. Far more tantalizing are the various designations as part of constellations that any- cuneiform tablets outlining astronomical one can learn to recognize. observations used by the Babylonians for Modern astronomers have divided the sky tracking the moon and developing a calendar. into 88 constellations, many of them fictitious— One of these is the MUL.APIN, which describes that is, they cover sky area, but contain no vis- the stars along the paths of the moon and ible stars.
    [Show full text]
  • Corona-Australis Dance I
    A&A 634, A98 (2020) Astronomy https://doi.org/10.1051/0004-6361/201936708 & c P. A. B. Galli et al. 2020 Astrophysics Corona-Australis DANCe I. Revisiting the census of stars with Gaia-DR2 data? P. A. B. Galli1, H. Bouy1, J. Olivares1, N. Miret-Roig1, L. M. Sarro2, D. Barrado3, A. Berihuete4, and W. Brandner5 1 Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hillaire, 33615 Pessac, France e-mail: [email protected] 2 Depto. de Inteligencia Artificial, UNED, Juan del Rosal, 16, 28040 Madrid, Spain 3 Centro de Astrobiología, Depto. de Astrofísica, INTA-CSIC, ESAC Campus, Camino Bajo del Castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain 4 Dept. Statistics and Operations Research, University of Cádiz, Campus Universitario Río San Pedro s/n, 11510 Puerto Real, Cádiz, Spain 5 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany Received 16 September 2019 / Accepted 11 December 2019 ABSTRACT Context. Corona-Australis is one of the nearest regions to the Sun with recent and ongoing star formation, but the current picture of its stellar (and substellar) content is not complete yet. Aims. We take advantage of the second data release of the Gaia space mission to revisit the stellar census and search for additional members of the young stellar association in Corona-Australis. Methods. We applied a probabilistic method to infer membership probabilities based on a multidimensional astrometric and photo- metric data set over a field of 128 deg2 around the dark clouds of the region. Results. We identify 313 high-probability candidate members to the Corona-Australis association, 262 of which had never been reported as members before.
    [Show full text]
  • Educator's Guide: Orion
    Legends of the Night Sky Orion Educator’s Guide Grades K - 8 Written By: Dr. Phil Wymer, Ph.D. & Art Klinger Legends of the Night Sky: Orion Educator’s Guide Table of Contents Introduction………………………………………………………………....3 Constellations; General Overview……………………………………..4 Orion…………………………………………………………………………..22 Scorpius……………………………………………………………………….36 Canis Major…………………………………………………………………..45 Canis Minor…………………………………………………………………..52 Lesson Plans………………………………………………………………….56 Coloring Book…………………………………………………………………….….57 Hand Angles……………………………………………………………………….…64 Constellation Research..…………………………………………………….……71 When and Where to View Orion…………………………………….……..…77 Angles For Locating Orion..…………………………………………...……….78 Overhead Projector Punch Out of Orion……………………………………82 Where on Earth is: Thrace, Lemnos, and Crete?.............................83 Appendix………………………………………………………………………86 Copyright©2003, Audio Visual Imagineering, Inc. 2 Legends of the Night Sky: Orion Educator’s Guide Introduction It is our belief that “Legends of the Night sky: Orion” is the best multi-grade (K – 8), multi-disciplinary education package on the market today. It consists of a humorous 24-minute show and educator’s package. The Orion Educator’s Guide is designed for Planetarians, Teachers, and parents. The information is researched, organized, and laid out so that the educator need not spend hours coming up with lesson plans or labs. This has already been accomplished by certified educators. The guide is written to alleviate the fear of space and the night sky (that many elementary and middle school teachers have) when it comes to that section of the science lesson plan. It is an excellent tool that allows the parents to be a part of the learning experience. The guide is devised in such a way that there are plenty of visuals to assist the educator and student in finding the Winter constellations.
    [Show full text]
  • SIMBA Observations of the R Corona Australis Molecular Cloud?,??
    A&A 409, 235–244 (2003) Astronomy DOI: 10.1051/0004-6361:20031115 & c ESO 2003 Astrophysics SIMBA observations of the R Corona Australis molecular cloud?;?? R. Chini1,K.K¨ampgen1;2,B.Reipurth2, M. Albrecht1,E.Kreysa3,R.Lemke1,M.Nielbock4, L. A. Reichertz3,A.Sievers5,andR.Zylka6 1 Astronomisches Institut der Ruhr-Universit¨at Bochum, Universit¨atsstrasse 150, 44780 Bochum, Germany 2 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA 3 Max Planck Institut f¨ur Radioastronomie, Auf dem H¨ugel 69, 53121 Bonn, Germany 4 SEST, European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile 5 IRAM, Avda. Divina Pastora 7, Nucleo Central, 18012 Granada, Spain 6 I. Physikalisches Institut, Universit¨at zu K¨oln, Z¨ulpicher Strasse 77, 50937 K¨oln, Germany Received 10 March 2003 / Accepted 16 July 2003 Abstract. We have mapped the R Corona Australis molecular cloud at 1.2 mm with SIMBA on SEST and detected 25 distinct dust emission peaks. While 7 of them coincide with positions of previously known young stars, 18 are seemingly not associated with any known stellar object. We discuss the nature of individual sources and conclude that there are at least four small concentrations of young objects located along the filamentary shaped cloud. A comparison with C18O data hints at the depletion of molecules in some of the cores. Our new results yield some conflicting arguments about whether star formation proceeds from north-west to south-east in the R Cr A cloud. Key words. ISM: dust, extinction – stars: circumstellar matter – stars: formation 1.
    [Show full text]
  • Constellation Is the Corona Australis
    CORONA AUSTRALIS, THE SOUTHERN CROWN Corona Australis is a constellation in the southern celestial hemisphere. Its Latin name means "southern crown", and it is the southern counterpart of Corona Borealis, the northern crown. One of the 48 constellations listed by the 2nd-century astronomer Ptolemy, it remains one of the 88 modern constellations. The Ancient Greeks saw Corona Australis as a wreath rather than a crown and associated it with Sagittarius or Centaurus. Other cultures have likened the pattern to a turtle, ostrich nest, a tent, or even a hut belonging to a rock hyrax (a shrewmouse; a small, well-furred, rotund animals with short tails). Although fainter than its northern namesake, the oval - or horseshoe-shaped pattern of its brighter stars renders it distinctive. Alpha and Beta Coronae Australis are its two brightest stars with an apparent magnitude of around 4.1. Epsilon Coronae Australis is the brightest example of a W Ursae Majoris variable in the southern sky (an eclipsing contact binary). Lying alongside the Milky Way, Corona Australis contains one of the closest star-forming regions to our Solar System —a dusty dark nebula known as the Corona Australis Molecular Cloud, lying about 430 light years away. Within it are stars at the earliest stages of their lifespan. The variable stars R and TY Coronae Australis light up parts of the nebula, which varies in brightness accordingly. Corona Australis is bordered by Sagittarius to the north, Scorpius to the west, Telescopium to the south, and Ara to the southwest. The three-letter abbreviation for the constellation, as adopted by the International Astronomical Union in 1922, is 'CrA'.
    [Show full text]
  • THE CONSTELLATION MUSCA, the FLY Musca Australis (Latin: Southern Fly) Is a Small Constellation in the Deep Southern Sky
    THE CONSTELLATION MUSCA, THE FLY Musca Australis (Latin: Southern Fly) is a small constellation in the deep southern sky. It was one of twelve constellations created by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman and it first appeared on a 35-cm diameter celestial globe published in 1597 in Amsterdam by Plancius and Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in Johann Bayer's Uranometria of 1603. It was also known as Apis (Latin: bee) for two hundred years. Musca remains below the horizon for most Northern Hemisphere observers. Also known as the Southern or Indian Fly, the French Mouche Australe ou Indienne, the German Südliche Fliege, and the Italian Mosca Australe, it lies partly in the Milky Way, south of Crux and east of the Chamaeleon. De Houtman included it in his southern star catalogue in 1598 under the Dutch name De Vlieghe, ‘The Fly’ This title generally is supposed to have been substituted by La Caille, about 1752, for Bayer's Apis, the Bee; but Halley, in 1679, had called it Musca Apis; and even previous to him, Riccioli catalogued it as Apis seu Musca. Even in our day the idea of a Bee prevails, for Stieler's Planisphere of 1872 has Biene, and an alternative title in France is Abeille. When the Northern Fly was merged with Aries by the International Astronomical Union (IAU) in 1929, Musca Australis was given its modern shortened name Musca. It is the only official constellation depicting an insect. Julius Schiller, who redrew and named all the 88 constellations united Musca with the Bird of Paradise and the Chamaeleon as mother Eve.
    [Show full text]
  • NANTEN Observations of Dense Cores in the Corona Australis Molecular Cloud
    PASJ: Publ. Astron. Soc. Japan 51, 911-918 (1999) NANTEN Observations of Dense Cores in the Corona Australis Molecular Cloud Yoshinori YONEKURA Department of Earth and Life Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531 E-mail (YY): [email protected] and Norikazu MIZUNO, Hiro SAITO, Akira MIZUNO, Hideo OGAWA* and Yasuo FUKUI Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya, ^64-8602 Downloaded from https://academic.oup.com/pasj/article/51/6/911/1467816 by guest on 30 September 2021 (Received 1999 August 26; accepted 1999 October 24) Abstract We carried out a C180 survey for dense molecular cores in the Corona Australis (CrA) molecular cloud with the NANTEN telescope. We observed 2.2 deg2 at a 2' grid spacing with a 2/7 beam, and 1980 positions were observed. We identified 8 C180 cores, whose typical line width, average column density, radius, mass, and average number density were 0.66 km s_1, 1.1 x 1022 cm-2, 0.13 pc, 18M®, and 1.4 x 104 cm-3, respectively. We found that AKomp, (Af(H2)), R, M, and n(H2) become larger along with an increase in the star-formation activity, whereas the ratio Mv-ir/M becomes smaller. A comparison of the present cores with those in Chamaeleon, Lupus, Ophiuchus, Taurus, and L 1333 indicates that star-forming cores tend to have a high column density, as well as a smaller MV-1T/M ratio. Key words: ISM: clouds — ISM: individual (Corona Australis Cloud) — ISM: molecules — stars: formation — radio lines: ISM 1. Introduction T CrA (FOe), TY CrA (B9e), and W CrA (Kl); there are also > 20 embedded IR sources, including the 'coro­ Recent observational studies have revealed that there net' cluster (Taylor, Storey 1984; Graham 1992; Wilking are a great variety of star-formation activities; only low- et al.
    [Show full text]