Archive for July, 2022

« Older Entries
Newer Entries »

The (unofficial) 2021 Journal Impact Factor for the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , on July 16, 2022 by telescoper

Since a few people have been asking about the Journal Impact Factor (JIF) for the Open Journal of Astrophysics, I thought I’d do a quick post in response.

When asked about this my usual reply is (a) to repeat the arguments why the impact factor is daft and (b) point out that the official JIF is calculated by Clarivate so it’s up to them to calculate it – us plebs don’t get a say.

On the latter point Clarivate takes its bibliometric data from the Web of Science (which it owns). I have applied on behalf of the Open Journal of Astrophysics to be listed in the Web of Science but it has not yet been listed.

Anyway, the fact that it’s out of my hands doesn’t stop people from asking so I thought I’d proceed with my own calculation not using Web of Science but instead using NASA/ADS (which probably underestimates citation numbers but which is freely available, so you can check the numbers using the interface here); the official NASA/ADS abbreviation for the Open Journal of Astrophysics is OJAp.

For those of you who can’t be bothered to look up the definition of an impact factor for a given year it is defined the sum of the citations for all papers published in the journal over the previous two-year period divided by the total number of papers published in that journal over the same period. It’s therefore the average citations per paper published in a two-year window. Since our first full year of publication was 2019, the first year for which we can calculate a JIF is 2021 (i.e. last year) which is defined using data from 2019 and 2020.

I stress again we don’t have an official Journal Impact Factor for the Open Journal of Astrophysics but one can calculate its value easily. In 2019 and 2020 we published 12 and 15 papers respectively, a 27. These papers were cited a total of 193 times in 2021. The journal impact factor for 2021 is therefore … roll on the drums… 193/27, which gives:

If you don’t believe me, you can check the numbers yourself. For comparison, the latest available Impact Factor (2020) for Monthly Notices of the Royal Astronomical Society is 5.29 and Astronomy & Astrophysics is 5.80. OJAp’s first full year of publication was 2019 (in which we published 12 papers) but we did publish one paper in 2018. Based on the 134 citations received to these 13 papers in 2020, our 2020 Journal Impact Factor was 10.31, much higher than MNRAS or A&A.

Furthermore, we published 32 papers in 2020 and 2021 which have so far received 125 citations in 2022. Our Journal Impact Factor for 2022 will therefore be at least 125/32= 3.91 and if those 32 papers are cited at the same for the rest of this year the 2022 JIF will be about 7.5.

Who knows, perhaps these numbers will shame Clarivate into giving us an official figure?

With so much bibliometric information available at the article level there is no reason whatsoever to pay any attention to such a crudely aggregated statistics at the journal level as the JIF. One should judge the contents, not the packaging. I am however fully aware that many people who hold the purse strings for research insist on publications in journals with a high JIF. If there was any fairness in the system they would be mandating astronomy publications in OJAp rather than MNRAS or A&A.

Anyway, it might annoy all the right people if I add a subtitle to the Open Journal of Astrophysics: “The World’s Leading Astrophysics Journal”…

8 Comments »

Tosca at the Bord Gáis

Posted in Opera with tags , , , , , , on July 15, 2022 by telescoper

Last night found me for the very first time at Dublin’s splendid Bord Gáis Energy Theatre, for a performance of Tosca by Irish National Opera, a tale of jealousy and murder set to gorgeous music by Giacomo Puccini.

Bord Gáis means “Gas Board”, by the way, but a rose by any other name would smell as sweet.

It’s been a while since I last went to an Opera and it was a last-minute decision to attend this one, but I heard good things about the opening night on Monday and managed to get a ticket. I’m very glad I did as there was much to enjoy, with some quite original variations on a very familiar story.

Tosca is an opera in three acts (which means two intervals wine breaks…). It’s a melodrama, and is set in Rome in 1800. Each Act takes place in a very specific location within the Eternal City. Act I is set in the Church of  Sant’Andrea della Valle, Act II in the Palazzo Farnese, and the final denouement of Act III takes place among the battlements at the top of the Castel Sant’ Angelo overlooking the Tiber.

Most productions of Tosca I have seen stick rigorously to a specific sense of time and place. In this one, directed by Michael Gieleta, the locations are suggested rather than reproduced directly and the costumes and interior design are generally 20th Century, with some sly references. The villainous Spoletta, for example, a police agent, is clearly dressed as a Jesuit. The shepherd boy in Act III appears as an angel, complete with wings, whose ghostly presence leads the prisoners on to their impending execution.

There is also some very ingenious staging, with a rotating set showing the torture scene in Act II while Scarpia and Tosca do their thing. The revolving structure also provides a very interesting alternative view of the end of Act III. I won’t say any more for fear of spoiling it for others…

Floria Tosca (Sinéad Campbell-Wallace, soprano) is a celebrated opera singer who is in love with an artist (and political radical) by the name of Mario Cavaradossi (Dimitri Pittas, tenor), who helps to hide an escaped political prisoner Cesare Angelotti (John Molloy, bass) while working on a painting in Act I. The odious Baron Scarpia (Tómas Tómasson, bass-baritone), Chief of Police, comes looking for the convict and decides to catch (in different ways) both Tosca and Cavaradossi: he lusts after the former and hates the latter.

In Act II, we find Scarpia at home eating dinner for one while Cavaradossi is being tortured in order to find out the location of the escapee. Tosca turns up to plead for his life, but she hasn’t bargained with the true depths of Scarpia’s depravity. He wants to have his way with her, and to put pressure on he lets her listen to the sound of her lover being tortured. She finally consents, in return for Scarpia’s promise to let Cavaradossi go and grant free passage to the two of them. This he seems to do, but while she is waiting for him to write the letter of conduct she sees a knife. Instead of letting Scarpia defile her, she grabs it and stabs him to death. Act III begins with Cavaradossi facing execution, sure he is about to die. Tosca is convinced that this is just a charade and that Scarpia ordered them to pretend to shoot Cavaradossi so he wouldn’t look like he was being merciful, which would be out of character. The firing squad fire and Cavaradossi falls. But it was no fake. He is dead. Tosca is distraught and bewildered. Shouts offstage reveal that the police have found Scarpia’s body and that Tosca must have murdered him. To avoid capture she hurls herself from the battlements. Her last words are “O Scarpia, avanti a Dio!” – “I’ll meet you before God, Scarpia”, though in this production we don’t actually see her jump…

The opera wasn’t particularly well received when it was first performed in 1900, being famously described by one critic as “a shabby little shocker”, but it has become a firm favourite with audiences around the world and is now acknowledged as a masterpiece of music drama. So how did Puccini manage to transform a penny-dreadful plot into a great work of art? I don’t think it’s hard to see why it works so well.

First and foremost, there’s the music, which  is wonderful throughout, but it is always plays an essential part in keeping everything moving. Of course there are the great arias: Vissi d’arte, Vissi d’amore sung by Tosca in Act II and E Lucevan le Stelle from Act III, sung by Cavaradossi; but even apart from those tremendous set-pieces, Puccini uses the music to draw out the psychology of the characters and underline the drama.

Although not usually associated with the use of leitmotifs, Puccini deploys them throughout: Scarpia’s arrival is announced with a suitably menacing theme that recurs whenever he is present or even just referred to.  This theme is actually the first thing we hear as the Opera starts. It also plays Scarpia out at the end of Act 1 when he sings his magnificently chilling Va Tosca over a setting of the Te Deum. Time does stand still for Tosca’s great Act II aria, the dramatic fulcrum of the Opera, but that just emphasises the pace of the rest of the piece. This is a work with no spare flesh or padding anywhere, and a perfect interplay between music and action. The moment when Tosca sees the knife with which she will kill Scarpia is signalled by the orchestra. And after Scarpia dies with Tosca preparing to make her getaway we hear, slower and deep down among the strings, Scarpia’s motif yet again. Even in death we feel he is still present…

Each of the three principal roles could have been very one-dimensional: Cavaradossi the good guy.; Scarpia the bad guy; Tosca the love interest. But all the characters have real credibility and depth. Cavaradossi is brave and generous, but he succumbs to despair before his death. No superhero this, just a man. Scarpia is a nasty piece of work all right, but at times he seems vulnerable; he is trapped by the same system he exploits. And then there’s the glamorous and loving, but not entirely likeable, Tosca who haughty and jealous, and at times spiteful. It is a truly shocking moment when she kills Scarpia. There’s no attempt to sanitise the violence of his death. It’s all so real. I guess that’s why this type of opera is called Verismo!

As for this production, I thought the principals were excellent: Dimitri Pittas seemed to be straining a bit in Act I but recovered and sang beautifully in Act III. Scarpia was suitably villainous and got a few pantomime boos at the end. A special mention must be made of the young shepherd (Joe Dwyer, treble) who was outstanding in a very difficult part for a young singer. Music director was Nil Venditti who bounced across the stage at the end to take the applause from a very appreciative audience.

There are still two performances of this production, on Saturday 16th and Sunday 17th.

1 Comment »

Characterization of JWST science performance from commissioning

Posted in The Universe and Stuff with tags , , , on July 14, 2022 by telescoper

I don’t suppose it will take very long for science papers based on the first data from JWST to start appearing on arXiv but I haven’t seen any yet. There is however a very important with an uncountable number of authors, led by Jane Rigby, that describes the commissioning process. Uncountable by me, that is.

Here is the abstract:

This document characterizes the actual science performance of the James Webb Space Telescope (JWST), as known on 12 July 2022. Following six months of commissioning to prepare JWST for science operations, the observatory is now fully capable of achieving the discoveries for which it was built. A key part of commissioning activities was characterizing the on-orbit performance of the observatory. Here we summarize how the performance of the spacecraft, telescope, science instruments, and ground system differ from pre-launch expectations. Almost across the board, the science performance of JWST is better than expected. In most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies.

Although it’s very long (60 pages) it’s well worth reading for an account of how meticulously the various calibrations etc were done. Various objects make cameo appearances, including Jupiter:

1 Comment »

James Webb: the wrong name for a Space Telescope

Posted in History, LGBTQ+, The Universe and Stuff with tags , , , on July 13, 2022 by telescoper

Following yesterday’s excitement about the new images from the James Webb Space Telescope I thought I’d share this video documentary that explains why the choice of name for this facility is highly inappropriate and should be changed. This is a matter I’ve blogged about previously, in fact, but the video is new.

2 Comments »

Those First Results from JWST

Posted in The Universe and Stuff with tags , , , , , on July 12, 2022 by telescoper

As promised in my post earlier today, we gathered in a small lecture theatre in Maynooth to watch the “reveal” of various new images and other data from the James Webb Space Telescope. The images are indeed wonderful and spectacular, but the video stream was excruciatingly bad to watch, with more technical glitches than I’ve had hot dinners. It was like an astronomical version of Acorn Antiques!

Anyway, you can find them all the new results together with explanations and descriptions here so Ill just put up a gallery here:

Carina Nebula
Stephan’s Quintet
Southern Ring Nebula
Slitless Spectroscopy of WASP 96-b

Those are the four results released today. This image was previewed last night and appeared in my post earlier today:

I couldn’t resist, however, adding this spectrum of a faint reddish galaxy in the above image:

This spectrum is taken using the NIRSpec instrument on JWST. The observed wavelength along the horizontal axis is measured in microns. If I’ve got the line identifications correct I think this galaxy is at an amazing redshift of about z=8.5. Amazing. High redshift galaxy spectra obtained are usually a lot rattier than this. I think this demonstrates that JWST is going to revolutionize the field of galaxy formation.

1 Comment »

The First Deep Field from JWST

Posted in Astronomy Lookalikes, The Universe and Stuff with tags , , , , , on July 12, 2022 by telescoper

I have to say that I didn’t stay up to watch the live stream of last night’s preview of this afternoon’s release of the first images from the James Webb Space Telescope. It started very late and I got sick of listening to the dreary music on the feed so went to bed. Nevertheless here is the first picture:

Credits: NASA, ESA, CSA, and STScI

This is a deep field image taken using JWST’s NIRCAM (Near-Infrared Camera). Note that the artifacts you see around some objects are diffraction spikes which occur around bright sources; their six-fold symmetry reflects the hexagonal structure built into the JWST’s mirror assembly. Sources sufficiently bright and compact enough to cause these spikes in deep field images are foreground stars: the extended, fainter objects are all much more distant galaxies.

The description from the NASA page is:

NASA’s James Webb Space Telescope has produced the deepest and sharpest infrared image of the distant universe to date. Known as Webb’s First Deep Field, this image of galaxy cluster SMACS 0723 is overflowing with detail.

Thousands of galaxies – including the faintest objects ever observed in the infrared – have appeared in Webb’s view for the first time. This slice of the vast universe is approximately the size of a grain of sand held at arm’s length by someone on the ground.

This deep field, taken by Webb’s Near-Infrared Camera (NIRCam), is a composite made from images at different wavelengths, totaling 12.5 hours – achieving depths at infrared wavelengths beyond the Hubble Space Telescope’s deepest fields, which took weeks. 

The image shows the galaxy cluster SMACS 0723 as it appeared 4.6 billion years ago. The combined mass of this galaxy cluster acts as a gravitational lens, magnifying much more distant galaxies behind it. Webb’s NIRCam has brought those distant galaxies into sharp focus – they have tiny, faint structures that have never been seen before, including star clusters and diffuse features. Researchers will soon begin to learn more about the galaxies’ masses, ages, histories, and compositions, as Webb seeks the earliest galaxies in the universe

Here is a close-up of one of the distorted galaxy images and othe features produced by gravitational lensing:

We’re having a special viewing in Maynooth this afternoon of the press conference which will unveil more new images from JWST – nice telescope, shame about the name. I may add comments on here if anything particularly exciting turns up. You can watch it here:

Let’s hope this one starts on time!

1 Comment »

The Consequences of Decoupling

Posted in Politics, The Universe and Stuff with tags , , , on July 11, 2022 by telescoper
Cosmology

I was struck by the similarity between the UK’s export performance post-Brexit (left) and the behaviour of radiative perturbations in the post-recombination Universe (right). It seems that, in different ways, they are both consequences of some form of decoupling…

Leave a comment »

Cosmological Constraints on Alternative Gravity Theories

Posted in The Universe and Stuff with tags , , , , , , , on July 11, 2022 by telescoper

The standard model of cosmology is based on Einstein’s theory of general relativity. In order to account for cosmological observations this has required the introduction of dark matter – which also helps explain the properties of individual galaxies – and dark energy. The result model, which I would describe as a working hypothesis, is rather successful but it is reasonable to question whether either or both of the dark components can be avoided by adopting an alternative theory of gravity instead of Einstein’s.

There is an interesting paper by Kris Pardo and David Spergel on arXiv that argues that none of the modifications of Einstein’s theory currently on the market is able to eliminate the need for dark matter. Here is the abstract of this paper:

It’s a more sophisticated version of an argument that has been going around at least in qualitative form for some time. The gist of it is that the distinctive pattern of fluctuations in the cosmic microwave background, observed by e.g. the Planck experiment, arise from coupling between baryons and photons in the early Universe. Similar features can be observed in the distribution of galaxies – where they are called Baryon Acoustic Oscilations (BAO) at a more recent cosmic epoch, but they are are much weaker. This is easily explicable if there is a dark matter component that dominates gravitational instability at late times but does not couple to photons via electromagnetic interactions. This is summed up in the following graphic (which I think I stole from a talk by John Peacock) based on data from about 20 years ago:

If there were no dark matter the coherent features seen in the power spectrum of the galaxy distribution would be much stronger; with dark matter dominating they are masked by the general growth of the collisionless component so their relative amplitude decreases.

The graphic shows how increasing the dark matter component from 0.1 to 0.3, while keeping the baryon component fixed, suppresses the wiggles corresponding to BAOs. The data suggest a dark matter contribution at the upper end of that range, consistent with the standard cosmology.

Of course if there are were no baryons at all there wouldn’t be fluctuations in either the CMB polarization or the galaxy distribution so both spectra would be smooth as shown in the graphic, but in that case there wouldn’t be anyone around to write about them as people are made of baryons.

This general conclusion is confirmed by the Pardo & Spergel paper, though it must be said that the argument doesn’t mean that modified gravity is impossible. It’s just that it seems nobody has yet thought of a specific model that satisfies all the constraints. That may change.

2 Comments »

New Publication at the Open Journal of Astrophysics

Posted in Open Access, The Universe and Stuff with tags , , , , , on July 10, 2022 by telescoper

Time to announce another new publication in the Open Journal of Astrophysics! This one, published last week, is the 9th paper in Volume 5 (2022) and the 57th in all.

The latest publication is entitled “Coronal Mass Ejection Image Edge Detection In Heliospheric Imager STEREO SECCHI Data” and is written by Marc Nichitiu of the Stony Brook School (NY, USA).  If you want to know more about the Solar observatory STEREO you can look here. SECCHI stands for “Sun-Earth Connection Coronal and Heliospheric Investigation”, which is a camera array on the STEREO spacecraft.

This paper is in the Solar and Stellar Astrophysics folder. It’s a slightly unusual paper because it is mainly software, so could have been in the Instrumentation and Methods for Astrophysics section.

Here is a screen grab of the overlay which includes the (very short) abstract:

 

 

You can click on the image to make it larger should you wish to do so. You can find the arXiv version of the paper here.

Leave a comment »

Phase Correlations and Cosmic Structure

Posted in Biographical, The Universe and Stuff with tags , , , on July 9, 2022 by telescoper

I’m indebted to a friend for tipping me off about a nice paper that appeared recently on the arXiv by Franco et al. with the title First measurement of projected phase correlations and large-scale structure constraints. The abstract is here:

Phase correlations are an efficient way to extract astrophysical information that is largely independent from the power spectrum. We develop an estimator for the line correlation function (LCF) of projected fields, given by the correlation between the harmonic-space phases at three equidistant points on a great circle. We make a first, 6.5σ measurement of phase correlations on data from the 2MPZ survey. Finally, we show that the LCF can significantly improve constraints on parameters describing the galaxy-halo connection that are typically degenerate using only two-point data.

 

I’ve worked on phase correlations myself (with a range of collaborators) – you can see a few of the papers here. Indeed I think it is fair to say I was one of the first people to explore ways of quantifying phase information in cosmology. Although I haven’t done anything on this recently (by which I mean in the last decade or so), other people have been developing very promising looking approaches (including the Line Correlation Function (LCF) explored in the above paper. In my view there is a lot of potential in this approach and as we await even more cosmological data and hopefully more people will look at this in future. In my opinion we still haven’t found the optimal way to exploit phase information statistically so there’s a lot of work to be done in this field.

Anyway, I thought I’d try to explain what phase correlations are and why they are important.

One of the challenges we cosmologists face is how to quantify the patterns we see in, for example, galaxy redshift surveys. In the relatively recent past the small size of the available data sets meant that only relatively crude descriptors could be used; anything sophisticated would be rendered useless by noise. For that reason, statistical analysis of galaxy clustering tended to be limited to the measurement of autocorrelation functions, usually constructed in Fourier space in the form of power spectra; you can find a nice review here.

Because it is so robust and contains a great deal of important information, the power spectrum has become ubiquitous in cosmology. But I think it’s important to realize its limitations.

Take a look at these two N-body computer simulations of large-scale structure:

The one on the left is a proper simulation of the “cosmic web” which is at least qualitatively realistic, in that in contains filaments, clusters and voids pretty much like what is observed in galaxy surveys.

To make the picture on the right I first  took the Fourier transform of the original  simulation. This approach follows the best advice I ever got from my thesis supervisor: “if you can’t think of anything else to do, try Fourier-transforming everything.”

Anyway each Fourier mode is complex and can therefore be characterized by an amplitude and a phase (the modulus and argument of the complex quantity). What I did next was to randomly reshuffle all the phases while leaving the amplitudes alone. I then performed the inverse Fourier transform to construct the image shown on the right.

What this procedure does is to produce a new image which has exactly the same power spectrum as the first. You might be surprised by how little the pattern on the right resembles that on the left, given that they share this property; the distribution on the right is much fuzzier. In fact, the sharply delineated features  are produced by mode-mode correlations and are therefore not well described by the power spectrum, which involves only the amplitude of each separate mode.

If you’re confused by this, consider the Fourier transforms of (a) white noise and (b) a Dirac delta-function. Both produce flat power-spectra, but they look very different in real space because in (b) all the Fourier modes are correlated in such away that they are in phase at the one location where the pattern is not zero; everywhere else they interfere destructively. In (a) the phases are distributed randomly.

The moral of this is that there is much more to the pattern of galaxy clustering than meets the power spectrum…

Leave a comment »

« Older Entries
Newer Entries »