Astronomy

What is a UBV source for stars or stellar objects?

What is a UBV source for stars or stellar objects?


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I was using the V19(VizieR) catalog and the main identifier of the stars was in terms of an 'ID' number which they mentioned as being 'Star number in UBV source' I have no idea what that means. How would I find a more common identifier say HD/HIP/HR number?


According to the associated paper (to get to this, click on the Bibcode link near the top right in VizieR), this refers to the source of the UBV photometry.

I believe the relevant references are the ones in the V/19/clusters table, e.g. for the second cluster (NGC 188) the reference is to Upgren, Mesrobian & Kerridge (1972). This does provide cross-references, but only to another catalogue of the cluster by Sandage (1962). It isn't particularly surprising that there aren't cross-references to more general catalogues, as identifying which star is which in such crowded fields can be challenging depending on how accurately positions and stellar properties are given.

Tracking some of the other references down is challenging, this is not helped by the fact that the ADS seems to have Romanized several of the names in various different ways, and searching for one Romanization does not return results for the others (at least, nothing came back for "Lavdovskij", although there are papers attributed to a "V. V. Lavdovsky" and "V. V. Lavdovskii"). I'm not sure how complete ADS coverage of Soviet publications (e.g. Izv. Glav. Astron. Obs. Pulkovo) is.


Massive Stars

Although quite rare, massive stars are a dominant source of light in galaxies. Their high surface temperatures mean that much of this light is emitted as ultraviolet photons, which ionize the gas in adjacent star-forming regions to produce beautiful nebulae such as the ones seen in the image above.

These UV photons also drive fast and dense wind outflows from massive stars, whose energy and momentum sculpt huge bubbles in the interstellar medium. This feedback continues throughout the stars' brief lifetimes, until they finally explode as supernovae, enriching the interstellar medium with nucleosynthetically-processed material and triggering new waves of star formation. This underscores the pivotal role played by massive stars in governing the evolution of the gas, dust, and stellar populations composing galaxies.

The Massive Stars Group at UW-Madison undertakes research into dynamical phenomena of massive stars &mdash winds, oscillations, rotation, and magnetic fields. Primarily, our focus is on the theory side of these phenomena, but we place a strong emphasis on matching theoretical predictions (typically, in the form of computer models) against observational data. Hence, we maintain strong collaborative ties with the wider massive-star community, and in particular are deeply involved in the MiMeS (Magnetism in Massive Stars) Project.

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What is a UBV source for stars or stellar objects? - Astronomy

Context. Age and mass determinations for isolated stellar objects remain model-dependent. While stellar interior and atmospheric theoretical models are rapidly evolving, we need a powerful tool to test them. Open clusters are good candidates for this role.
Aims: We aim to create a fiducial sequence of stellar objects for testing stellar and atmospheric models.
Methods: We complement previous studies on the Hyades multiplicity by Lucky Imaging observations with the AstraLux Norte camera. This allows us to exclude possible binary and multiple systems with companions outside a 2-7 AU separation and to create a single-star sequence for the Hyades. The sequence encompasses 250 main-sequence stars ranging from A5V to M6V. Using the Tool for Astrophysical Data Analysis (TA-DA), we create various theoretical isochrones applying different combinations of interior and atmospheric models. We compare the isochrones with the observed Hyades single-star sequence on J vs. J-K s , J vs. J-H, and K s vs. H-K s color-magnitude diagrams. As a reference we also compute absolute fluxes and magnitudes for all stars from X-ray to mid-infrared based on photometric measurements available in the literature(ROSAT X-ray, GALEX UV, APASS gri, 2MASS JHK s , and WISE W1 to W4).
Results: We find that combinations of both PISA and DARTMOUTH stellar interior models with BT-Settl 2010 atmospheric models describe the observed sequence well. We use PISA in combination with BT-Settl 2010 models to derive theoretical predictions for physical parameters (T eff , mass, log g) of 250 single stars in the Hyades. The full sequence covers the mass range of 0.13-2.30 M ⊙ , and effective temperatures between 3060 K and 8200 K.
Conclusions: Within the measurement uncertainties, the current generation of models agree well with the single-star sequence. The primary limitations are the uncertainties in the measurement of the distances to individual Hyades members, and uncertainties in the photometry. Gaia parallaxes, photometry, and spectroscopy will greatly reduce the uncertainties in particular at the lowest mass range, and will enable us to test model predictions with greater confidence. Additionally, a small (

0.05 mag) systematic offset can be noted in J vs. J-K and K vs. H-K diagrams - the observed sequence is shifted to redder colors than the theoretical predictions.


Contents

The universe can be viewed as having a hierarchical structure. [2] At the largest scales, the fundamental component of assembly is the galaxy. Galaxies are organized into groups and clusters, often within larger superclusters, that are strung along great filaments between nearly empty voids, forming a web that spans the observable universe. [3]

Galaxies have a variety of morphologies, with irregular, elliptical and disk-like shapes, depending on their formation and evolutionary histories, including interaction with other galaxies, which may lead to a merger. [4] Disc galaxies encompass lenticular and spiral galaxies with features, such as spiral arms and a distinct halo. At the core, most galaxies have a supermassive black hole, which may result in an active galactic nucleus. Galaxies can also have satellites in the form of dwarf galaxies and globular clusters. [5]

The constituents of a galaxy are formed out of gaseous matter that assembles through gravitational self-attraction in a hierarchical manner. At this level, the resulting fundamental components are the stars, which are typically assembled in clusters from the various condensing nebulae. [6] The great variety of stellar forms are determined almost entirely by the mass, composition and evolutionary state of these stars. Stars may be found in multi-star systems that orbit about each other in a hierarchical organization. A planetary system and various minor objects such as asteroids, comets and debris, can form in a hierarchical process of accretion from the protoplanetary disks that surround newly formed stars.

The various distinctive types of stars are shown by the Hertzsprung–Russell diagram (H–R diagram)—a plot of absolute stellar luminosity versus surface temperature. Each star follows an evolutionary track across this diagram. If this track takes the star through a region containing an intrinsic variable type, then its physical properties can cause it to become a variable star. An example of this is the instability strip, a region of the H-R diagram that includes Delta Scuti, RR Lyrae and Cepheid variables. [7] The evolving star may eject some portion of its atmosphere to form a nebula, either steadily to form a planetary nebula or in a supernova explosion that leaves a remnant. Depending on the initial mass of the star and the presence or absence of a companion, a star may spend the last part of its life as a compact object either a white dwarf, neutron star, or black hole.

The IAU definitions of planet and dwarf planet require that a Sun-orbiting astronomical body has undergone the rounding process to reach a roughly spherical shape, an achievement known as hydrostatic equilibrium. The same spheroidal shape can be seen from smaller rocky planets like Mars to gas giants like Jupiter.

Any natural Sun-orbiting body that has not reached hydrostatic equilibrium is classified by the IAU as a small Solar System body (SSB). These come in many non-spherical shapes which are lumpy masses accreted haphazardly by in-falling dust and rock not enough mass falls in to generate the heat needed to complete the rounding. Some SSSBs are just collections of relatively small rocks that are weakly held next to each other by gravity but are not actually fused into a single big bedrock. Some larger SSSBs are nearly round but have not reached hydrostatic equilibrium. The small Solar System body 4 Vesta is large enough to have undergone at least partial planetary differentiation.

Stars like the Sun are also spheroidal due to gravity's effects on their plasma, which is a free-flowing fluid. Ongoing stellar fusion is a much greater source of heat for stars compared to the initial heat released during formation.

The table below lists the general categories of bodies and objects by their location or structure.


100,000 star nurseries mapped in first-of-its-kind survey

Stellar nurseries, the cauldrons of gas and dust where stars are forged, are far more diverse than astronomers first thought, according to a new, first-of-its kind survey.

Astronomers at the Physics at High Angular Resolution in Nearby Galaxies (PHANGS) project have systematically charted more than 100,000 nurseries across 90 galaxies, and found that each one is far more unique than first thought.

Stars can take tens of millions of years to form — growing from billowing clouds of turbulent dust and gas into gently glowing protostars, before finally materializing into gigantic orbs of fusion-powered plasma like our sun. But how quickly this process depletes a nursery's store of gas and dust, and how many stars are subsequently able to form in a given place, depends on a stellar nursery's location in a galaxy.

"We used to think that all stellar nurseries across every galaxy must look more or less the same, but this survey has revealed that this is not the case, and stellar nurseries change from place to place," lead author Adam Leroy, associate professor of astronomy at The Ohio State University, said in a statement. "These nurseries are responsible for building galaxies and making planets, and they're just an essential part in the story of how we got here."

The five-year survey, conducted across a section of the cosmos known as the nearby universe because of its proximity to our own galaxy, used the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescope located in Chile's Atacama Desert. By conducting their survey in the radio part of the electromagnetic spectrum, rather than the optical part, the astronomers could focus on the faint glow from the dust and gas of the dark and dense molecular clouds, as opposed to the visible light from the young stars birthed by them.

This allowed the researchers to study how a star's home cloud shapes its formation.

"To understand how stars form, we need to link the birth of a single star back to its place in the universe. It's like linking a person to their home, neighborhood, city and region. If a galaxy represents a city, then the neighborhood is the spiral arm, the house the star-forming unit, and nearby galaxies are neighboring cities in the region," PHANGS principal investigator Eva Schinnerer, an astronomer at the Max Planck Institute for Astronomy, said in the statement. "These observations have taught us that the 'neighborhood' has small but pronounced effects on where and how many stars are born."

They found that stars are forged differently depending on whether the molecular clouds that create them are located in galactic discs, stellar bars, spiral arms or galactic centers.

"Clouds in the dense central regions of galaxies tend to be more massive, denser and more turbulent than clouds that reside in the quiet outskirts of a galaxy," said co-author Annie Hughes, an astronomer at L'Institut de Recherche en Astrophysique et Planétologie. "The life cycle of clouds also depends on their environment. How fast a cloud forms stars and the process that ultimately destroys the cloud both seem to depend on where the cloud lives."

Next, the team will try to figure out what this variation could mean for the formation of stars and planets, as well as for our own place in the universe.

"This is the first time we have gotten a clear view of the population of stellar nurseries across the whole nearby universe. In that sense, it's a big step towards understanding where we come from," Leroy said in the statement. "While we now know that stellar nurseries vary from place to place, we still do not know why or how these variations affect the stars and planets formed. These are questions that we hope to answer in the near future."

The researchers presented their findings on Tuesday (June 8) at the online summer meeting of the American Astronomical Society, and they published their findings April 15 on the preprint server arXiv, so the study has yet to be peer-reviewed.

Originally published on Live Science.

Stellar nurseries, the cauldrons of gas and dust where stars are forged, are far more diverse than astronomers first thought, according to a new, first-of-its kind survey.

Astronomers at the Physics at High Angular Resolution in Nearby Galaxies (PHANGS) project have systematically charted more than 100,000 nurseries across 90 galaxies, and found that each one is far more unique than first thought.

Stars can take tens of millions of years to form — growing from billowing clouds of turbulent dust and gas into gently glowing protostars, before finally materializing into gigantic orbs of fusion-powered plasma like our sun. But how quickly this process depletes a nursery's store of gas and dust, and how many stars are subsequently able to form in a given place, depends on a stellar nursery's location in a galaxy.

"We used to think that all stellar nurseries across every galaxy must look more or less the same, but this survey has revealed that this is not the case, and stellar nurseries change from place to place," lead author Adam Leroy, associate professor of astronomy at The Ohio State University, said in a statement. "These nurseries are responsible for building galaxies and making planets, and they're just an essential part in the story of how we got here."

The five-year survey, conducted across a section of the cosmos known as the nearby universe because of its proximity to our own galaxy, used the Atacama Large Millimeter/Submillimeter Array (ALMA) radio telescope located in Chile's Atacama Desert. By conducting their survey in the radio part of the electromagnetic spectrum, rather than the optical part, the astronomers could focus on the faint glow from the dust and gas of the dark and dense molecular clouds, as opposed to the visible light from the young stars birthed by them.

This allowed the researchers to study how a star's home cloud shapes its formation.

"To understand how stars form, we need to link the birth of a single star back to its place in the universe. It's like linking a person to their home, neighborhood, city and region. If a galaxy represents a city, then the neighborhood is the spiral arm, the house the star-forming unit, and nearby galaxies are neighboring cities in the region," PHANGS principal investigator Eva Schinnerer, an astronomer at the Max Planck Institute for Astronomy, said in the statement. "These observations have taught us that the 'neighborhood' has small but pronounced effects on where and how many stars are born."

They found that stars are forged differently depending on whether the molecular clouds that create them are located in galactic discs, stellar bars, spiral arms or galactic centers.

"Clouds in the dense central regions of galaxies tend to be more massive, denser and more turbulent than clouds that reside in the quiet outskirts of a galaxy," said co-author Annie Hughes, an astronomer at L'Institut de Recherche en Astrophysique et Planétologie. "The life cycle of clouds also depends on their environment. How fast a cloud forms stars and the process that ultimately destroys the cloud both seem to depend on where the cloud lives."

Next, the team will try to figure out what this variation could mean for the formation of stars and planets, as well as for our own place in the universe.


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Magnitude systems

Problems arise when only one colour index is observed. If, for instance, a star is found to have, say, a BV colour index of 1.0 (i.e., a reddish colour), it is impossible without further information to decide whether the star is red because it is cool or whether it is really a hot star whose colour has been reddened by the passage of light through interstellar dust. Astronomers have overcome these difficulties by measuring the magnitudes of the same stars through three or more filters, often U (ultraviolet), B, and V (see UBV system).

Observations of stellar infrared light also have assumed considerable importance. In addition, photometric observations of individual stars from spacecraft and rockets have made possible the measurement of stellar colours over a large range of wavelengths. These data are important for hot stars and for assessing the effects of interstellar attenuation.


UBV photometric system

The UBV photometric system, also called the Johnson system (or Johnson-Morgan system), is a wide band photometric system for classifying stars according to their colors. It is the first known standardized photoelectric photometric system. The letters U, B, and V stand for ultraviolet, blue, and visual magnitudes, which are measured for a star in order to classify it in the UBV system. [1] The choice of colors on the blue end of the spectrum is because of the bias that photographic film has for those colors. It was introduced in the 1950s by American astronomers Harold Lester Johnson and William Wilson Morgan. A 13" telescope and the 82" telescope at McDonald Observatory were used to define the system. [1] [2]

The filters are selected so that the mean wavelengths of response functions are 364 nm for U, 442 nm for B, 540 nm for V. The zero point of the B−V and U−B color indices were defined such as to be about zero for A0 main sequence stars not affected by interstellar reddening. [1]

The UBV system has some disadvantages. The short wavelength cutoff of the U filter is defined mainly by the terrestrial atmosphere rather than the filter itself thus, it (and observed magnitudes) can vary with altitude and atmospheric conditions. [3] However, a large number of measurements have been made in this system, including many of the bright stars. [4]


Best Overall Astronomy App: Sky Safari

If you’re new to astronomy, Sky Safari (Free) is a great place to start. The app offers the standard night sky map with AR constellation overlay, as well as tons of helpful information about celestial bodies (including over 120,000 stars and hundreds of other objects) in its sleek and well-organized interface. I recommend toggling the app’s Compass option for automatic real-time tracking (so you don’t have to manually move it). You can learn more about an object by tapping on it, then on Selection, and Object Info from there, you’ll see the object’s name and photo, as well as information about its appearance, mythology, historical observations, evolution, and more.

The coolest feature of Sky Safari is one that’s more fun than function: time travel. No, I’m not talking about Doctor Who or Marty McFly, but the app can show you an animated simulation of how celestial contents moved as you “travel” back through time. I let the app run for about 45 minutes on my phone and it went back past 45,000 B.C.E (and I’m sure it could go further). You can even toggle night mode and view the night’s expected astronomical events, like where to see planets or if the ISS will be visible. Sky Safari is a fun, immersive choice for beginner and intermediate stargazers alike, and it makes learning about space easy.


A pair of lonely planet-like objects born like stars

Artist's composition of the two brown dwarfs, in the foreground Oph 98B in purple, in the background Oph 98A in red. Oph 98A is the more massive and therefore more luminous and hotter of the two. The two objects are surrounded by the molecular cloud in which they were formed. Credit: University of Bern/Thibaut Roger

An international research team led by the University of Bern has discovered an exotic binary system composed of two young planet-like objects, orbiting around each other from a very large distance. Although these objects look like giant exoplanets, they formed in the same way as stars, proving that the mechanisms driving star formation can produce rogue worlds in unusual systems deprived of a Sun.

Star-forming processes sometimes create mysterious astronomical objects called brown dwarfs, which are smaller and colder than stars, and can have masses and temperatures down to those of exoplanets in the most extreme cases. Just like stars, brown dwarfs often wander alone through space, but can also be seen in binary systems, where two brown dwarfs orbit one another and travel together in the galaxy.

Researchers led by Clémence Fontanive from the Center for Space and Habitability (CSH) and the NCCR PlanetS discovered a curious starless binary system of brown dwarfs. The system CFHTWIR-Oph 98 (or Oph 98 for short) consists of the two very low-mass objects Oph 98 A and Oph 98 B. It is located 450 light years away from Earth in the stellar association Ophiuchus. The researchers were surprised by the fact that Oph 98 A and B are orbiting each other from a strikingly large distance, about 5 times the distance between Pluto and the Sun, which corresponds to 200 times the distance between the Earth and the Sun. The study has just been published in The Astrophysical Journal Letters.

Extremely low masses and a very large separation

The pair is a rare example of two objects similar in many aspects to extra-solar giant planets, orbiting around each other with no parent star. The more massive component, Oph 98 A, is a young brown dwarf with a mass of 15 times that of Jupiter, which is almost exactly on the boundary separating brown dwarfs from planets. Its companion, Oph 98 B, is only 8 times heavier than Jupiter.

Components of binary systems are tied by an invisible link called gravitational binding energy, and this bond gets stronger when objects are more massive or closer to one another. With extremely low masses and a very large separation, Oph 98 has the weakest binding energy of any binary system known to date.

Discovery thanks to data from Hubble

Clémence Fontanive and her colleagues discovered the companion to Oph 98 A using images from the Hubble Space Telescope. Fontanive says: "Low-mass brown dwarfs are very cold and emit very little light, only through infrared thermal radiation. This heat glow is extremely faint and red, and brown dwarfs are hence only visible in infrared light." Furthermore, the stellar association in which the binary is located, Ophiuchus, is embedded in a dense, dusty cloud which scatters visible light. "Infrared observations are the only way to see through this dust," explains the lead researcher. "Detecting a system like Oph 98 also requires a camera with a very high resolution, as the angle separating Oph 98 A and B is a thousand times smaller than the size of the moon in the sky," she adds. The Hubble Space Telescope is among the few telescopes capable of observing objects as faint as these brown dwarfs, and able to resolve such tight angles.

Because brown dwarfs are cold enough, water vapor forms in their atmospheres, creating prominent features in the infrared that are commonly used to identify brown dwarfs. However, these water signatures cannot be easily detected from the surface of the Earth. Located above the atmosphere in the vacuum of space, Hubble allows to probe the existence of water vapor in astronomical objects. Fontanive explains: "Both objects looked very red and showed clear signs of water molecules. This immediately confirmed that the faint source we saw next to Oph 98 A was very likely to also be a cold brown dwarf, rather than a random star that happened to be aligned with the brown dwarf in the sky."

The team also found images in which the binary was visible, collected 14 years ago with the Canada-France-Hawaii Telescope (CFHT) in Hawaii. "We observed the system again this summer from another Hawaiian observatory, the United Kingdom Infra-Red Telescope. Using these data, we were able to confirm that Oph 98 A and B are moving together across the sky over time, relative to other stars located behind them, which is evidence that they are bound to each other in a binary pair," explains Fontanive.

An atypical result of star formation

The Oph 98 binary system formed only 3 million years ago in the nearby Ophiuchus stellar nursery, making it a newborn on astronomical timescales. The age of the system is much shorter than the typical time needed to build planets. Brown dwarfs like Oph 98 A are formed by the same mechanisms as stars. Despite Oph 98 B being the right size for a planet, the host Oph 98 A is too small to have a sufficiently large reservoir of material to build a planet that big. "This tells us that Oph 98 B, like its host, must have formed through the same mechanisms that produce stars and shows that the processes that create binary stars operate on scale-down versions all the way down to these planetary masses," comments Clémence Fontanive.

With the discovery of two planet-like worlds—already uncommon products of star formation—bound to each other in such an extreme configuration, "we are really witnessing an incredibly rare output of stellar formation processes," as Fontanive describes.