What Makes Us Human? The Answer May be Found in Overlooked DNA (Biology)

Our DNA is very similar to that of the chimpanzee, which in evolutionary terms is our closest living relative. Stem cell researchers at Lund University in Sweden have now found a previously overlooked part of our DNA, so-called non-coded DNA, that appears to contribute to a difference which, despite all our similarities, may explain why our brains work differently. The study is published in the journal Cell Stem Cell.

The chimpanzee is our closest living relative in evolutionary terms and research suggests our kinship derives from a common ancestor. About five to six million years ago, our evolutionary paths separated, leading to the chimpanzee of today, and Homo Sapiens, humankind in the 21st century.

In a new study, stem cell researchers at Lund examined what it is in our DNA that makes human and chimpanzee brains different – and they have found answers.

“Instead of studying living humans and chimpanzees, we used stem cells grown in a lab. The stem cells were reprogrammed from skin cells by our partners in Germany, the USA and Japan. Then we examined the stem cells that we had developed into brain cells”, explains Johan Jakobsson, professor of neuroscience at Lund University, who led the study.

“The basis for the human brain’s evolution are genetic mechanisms that are probably a lot more complex than previously thought”

Using the stem cells, the researchers specifically grew brain cells from humans and chimpanzees and compared the two cell types. The researchers then found that humans and chimpanzees use a part of their DNA in different ways, which appears to play a considerable role in the development of our brains.

“The part of our DNA identified as different was unexpected. It was a so-called structural variant of DNA that were previously called “junk DNA”, a long repetitive DNA string which has long been deemed to have no function. Previously, researchers have looked for answers in the part of the DNA where the protein-producing genes are – which only makes up about two per cent of our entire DNA – and examined the proteins themselves to find examples of differences.”

Microscope image of neural stem cells
Neural stem cells from chimpanzees (Photo: Johan Jakobsson)

The new findings thus indicate that the differences appear to lie outside the protein-coding genes in what has been labelled as “junk DNA”, which was thought to have no function and which constitutes the majority of our DNA.

“This suggests that the basis for the human brain’s evolution are genetic mechanisms that are probably a lot more complex than previously thought, as it was supposed that the answer was in those two per cent of the genetic DNA. Our results indicate that what has been significant for the brain’s development is instead perhaps hidden in the overlooked 98 per cent, which appears to be important. This is a surprising finding.”

The stem cell technique used by the researchers in Lund is revolutionary and has enabled this type of research. The technique was recognised by the 2012 Nobel Prize in Physiology or Medicine. It was the Japanese researcher Shinya Yamanaka who discovered that specialised cells can be reprogrammed and developed into all types of body tissue. And in the Lund researchers’ case, into brain cells. Without this technique, it would not have been possible to study the differences between humans and chimpanzees using ethically defensible methods.

Why did the researchers want to investigate the difference between humans and chimpanzees?

“I believe that the brain is the key to understanding what it is that makes humans human. How did it come about that humans can use their brain in such a way that they can build societies, educate their children and develop advanced technology? It is fascinating!”

Johan Jakobsson believes that in the future the new findings may also contribute to genetically-based answers to questions about psychiatric disorders, such as schizophrenia, a disorder that appears to be unique to humans.

“But there is a long way to go before we reach that point, as instead of carrying out further research on the two per cent of coded DNA, we may now be forced to delve deeper into all 100 per cent – a considerably more complicated task for research”, he concludes.

Featured image: Mostphotos


Publication:

Link to the article in Cell Stem Cell:

cis-acting structural variation at the ZNF558 locus controls a gene regulatory network in human brain development


Provided by Lund University

A Billion-year Soul-burning puzzle: Who Made Cheilanthanes? (Paleontology)

PhD student Tharika Liyanage is on a quest to solve a molecule mystery that dates back billions of years, writes Lauren Pay.

Everyone has a different soul-burning question.

It might be ‘what is the meaning of life?’ or ‘will I ever find love?’

Such questions sit heavy on the heart, and could, in some cases, remain forever unanswered.

Most of us must learn to live with the idea of never knowing. But not Tharika Liyanage. The ANU PhD researcher has decided that instead of waiting around, she will answer her soul-burning question: who makes cheilanthanes?

A cheilan-what now?

Exactly.

They may be almost invisible, but cheilanthanes are a big deal. These fossilised biological molecules dating back billions of years are found in almost every rock and oil on Earth. There’s probably more than 500 billion tonnes of the stuff. That’s more mass than if we combined all the plants, animals, insect, people and fungi alive today.

The problem is we don’t know who made cheilanthanes. Liyanage is on a quest to find out where they come from.

“The whole mystery was so intriguing,” Liyanage says.

“Previous research on this topic had stalled because they were looking in the past, but I’m searching for the source in the present.”

One is easily caught up in the drama of this mystery, even before knowing what a cheilanthane is, or why they are so important.

But important they are. This stealthy molecule is likely to play a crucial role in challenging our ideas of how life evolved on our planet.

In essence, a cheilanthane is a hydrocarbon. It can also be classified as a biomarker, which are fossilised markers of certain molecules preserved in the rock record.

“With their presence, we can start to make deductions about past ecosystems,” Liyanage explains.

“Cheilanthanes are so interesting because they are found in the rock record as far back as 1.64 billion years ago, and all through the geological record to more recently.”

Previous research has indicated the source of these cheilanthanes is extinct, but Liyanage has discovered that might not be the case.

Her quest for answers took her around the globe. Using a technique she invented for this purpose, she found evidence of cheilanthanes in the European Alps, and even as far as Antarctica.

“When we first realised that there was evidence suggesting cheilanthane producing organisms still existed I was dumbfounded,” Liyanage says.

“We spent such a long time looking so I was nervous we were never going to find them. It really was one of those Eureka moments.”

This important finding has allowed her to link the biomarker with a biological source.

“We can now work to piece together past ecosystems in Earth’s history,” Liyanage explains.

This discovery is the topic of Liyanage’s entry to the Three Minute Thesis (3MT) competition. Having won the ANU round and then gone head-to-head with 54 other presenters in the semi-finals, Liyanage then placed second at the Asia-Pacific final.

It’s an incredible feat for an incredible young researcher on an incredible quest.

However, Liyanage doesn’t intend for the story of cheilanthanes to end here.

“There are still lots of unanswered questions about why they are made, and how this might be used to our benefit,” she says.

She now has many more soul-burning questions about this amazing molecule, and will continue her research to answer as many as she can.

Watch Tharika Liyanage’s Three Minute Thesis presentation here.

Featured image: PhD researcher Tharika Liyanage is on the hunt for a mysterious molecule that may rewrite the books on evolution . Photo : ANU


Provided by ANU

Jet From Giant Galaxy M87: Computer Modelling Explains Black Hole Observations (Cosmology)

The black hole of the giant galaxy M87 shoots out an enormous jet of particles. A theoretical model of this jet has now been developed that fits astronomical observations very well.

The galaxy Messier 87 (M87) is located 55 million light years away from Earth in the Virgo constellation. It is a giant galaxy with 12,000 globular clusters, making the Milky Way’s 200 globular clusters appear modest in comparison.

A black hole of six and a half billion sun masses is harboured at the centre of M87. It is the first black hole for which an image exists, created in 2019 by the international research collaboration Event Horizon Telescope.

This black hole shoots a jet of plasma at near the speed of light, a so-called relativistic jet, on a scale of 6,000 light years. The tremendous energy needed to power this jet probably originates from the gravitational pull of the black hole, but how a jet like this comes about and what keeps it stable across the enormous distance is not yet fully understood.

Three-dimensional supercomputer simulations

The black hole of the galaxy M87 attracts matter that rotates in a disc in ever smaller orbits until it is swallowed by the black hole. The jet is launched from the centre of this disc surrounding M87.

Theoretical physicists at Goethe University Frankfurt together with scientists from the Harvard University, Julius-Maximilians-Universität Würzburg (JMU), University of Shanghai, the University College London, the University of Amsterdam, the Radboud University Nijmegen, and the Max Planck Institute for Radio Astronomy in Bonn, have now modelled this region in great detail.

They used highly sophisticated three-dimensional supercomputer simulations that use the staggering amount of a million CPU hours per simulation and had to simultaneously solve the equations of general relativity by Albert Einstein, the equations of electromagnetism by James Maxwell, and the equations of fluid dynamics by Leonhard Euler.

Model corresponds remarkably well with observations

The result was a model in which the values calculated for the temperatures, the matter densities and the magnetic fields correspond remarkably well with what deduced from the astronomical observations.

On this basis, scientists were able to track the complex motion of photons in the curved spacetime of the innermost region of the jet and translate this into radio images. They were then able to compare these computer modelled images with the observations made using numerous radio telescopes and satellites over the past three decades.

Dr Alejandro Cruz-Osorio, lead author of the study, comments: “Our theoretical model of the electromagnetic emission and of the jet morphology of M87 matches surprisingly well with the observations in the radio, optical and near-infrared regime. This tells us that the supermassive black hole of M87 is probably highly rotating and that the plasma is strongly magnetized in the jet, accelerating particles out to scales of thousands of light years.”

Professor Luciano Rezzolla, Institute for Theoretical Physics at Goethe University Frankfurt, remarks: “The fact that the images we calculated are so close to the astronomical observations is another important confirmation that Einstein’s theory of general relativity is the most precise and natural explanation for the existence of supermassive black holes in the centre of galaxies. While there is still room for alternative explanations, the findings of our study have made this room much smaller.”

Dr Christian M. Fromm, who moved from Harvard University to the JMU Chair of Astronomy as head of a junior research group at the beginning of October 2021, was also involved in the study: “In the coming years we will further investigate the formation of jets and the underlying particle acceleration mechanisms throughout the entire electromagnetic spectrum using modern computer simulations and state-of-the art observations within the newly founded DFG Research Unit on Relativistic Jets at the Julius Maximilians University Wuerzburg and partner institutes in Germany and abroad”.

Featured image: The theoretical model (left) and the astronomical observations of the launching site of the relativistic jet of M87 are a very good match. (Image: Alejandro Cruz-Osorio / Goethe Universität Frankfurt)


Publication

Alejandro Cruz-Osorio, Christian M. Fromm, Yosuke Mizuno, Antonios Nathanail, Ziri Younsi, Oliver Porth, Jordy Davelaar, Heino Falcke, Michael Kramer, Luciano Rezzolla: State-of-the-art energetic and morphological modelling of the launching site of the M87 jet. Nature Astronomy 2021, https://doi.org10.1038/s41550-021-01506-w


Provided by Universität Wuerzburg

Researcher Argues For Existence of Companion Candidate Stars to the Eclipsing Binary Algol (Cosmology)

Dr. Lauri Jetsu from the University of Helsinki has analyzed observations of Algol. He argues that Algol has many companion stars which have not been detected from earlier observations. The results have been published in The Astrophysical Journal.

Algol is an eclipsing binary, where the two stars Algol A and Algol B orbit around their common center of mass. Their orbital period is 2.867 days. The abbreviation for this binary system is Algol AB.

Algol’s primary eclipses occur when the dimmer Algol B partially covers the brighter Algol A. These primary eclipses last ten hours, and they can be observed with naked eye. Goodricke (1783) determined Algol’s orbital period from naked eye observations of these events. The primary eclipses would be repeated regularly exactly after 2.867 days, if nothing disturbed the motions of Algol AB binary system. All these future eclipses could be computed from the multiples of the constant period 2.867 days.

The presence of a third member Algol C in this multiple star system was confirmed in late 1950s. Algol C and Algol AB orbit around their common center of mass. One round takes 1.86 years. The orbital motions of Algol C and Algol AB cause a light travel time effect. We observe the primary eclipses earlier when Algol AB is closer to us, and later when Algol AB is further away from us. During every 1.86 years round, Algol C causes the same regular positive and negative time shifts in the observed eclipse epochs of Algol AB. The range of these time shifts is only about nine minutes. Due to these time shifts, the observed eclipse epochs (O=Observed) differ from the computed constant period eclipse epochs (C=Computed). These differences are called the O-C data.

There may be even four or five new companions

Lauri Jetsu analyzed the O-C data of Algol between November 1782 and October 2018. He applied his recently formulated discrete chi-square method to these data. This method is designed for detecting regular periodic signals. These detections succeed even if the signals are superimposed on an irregular aperiodic trend. From O-C data of Algol AB, the discrete chi-square method can detect the light travel time effect signals of five or six companion star candidates. The O-C data alone can not be used to establish the exact number of these candidates. One of these candidates is the known “old” companion Algol C. The orbital periods of the other four or five “new” companion star candidates are between 20 and 219 years.

“These stars are candidates until new observations confirm their existence,” says Jetsu. He also shows that the periodic signals of these candidates can predict the observed Algol’s O-C changes.

Why have these candidates not been detected earlier?

Algol is so close to the sun that astronomers can observe its eclipses with naked eye. Algol’s new companion candidate stars would be literally in our backyard.

“The paradox is that Algol is ‘too bright,'” says Jetsu. Algol can hide these new companion candidate stars even from our most powerful modern space telescopes, just like our sun can hide all other stars during daytime, says Jetsu. He points out that, for example, the cutting-edge equipment onboard the Gaia satellite could not detect Algol’s new companion candidates. Jetsu argues that future interferometric observations may be used to directly confirm the existence of at least some of these new Algol’s companion candidates.

Featured image: (a) Algol’s O-C data (red circles). The time-axis units are days between November 1782 and October 2018. The green continuous line shows the five signal model for the first 226 years of data before the dotted vertical line. The data minus model differences are offset from zero to -0.3 (blue circles). (b) The last 15 years of O-C data. Beyond the vertical dotted line begins the prediction for the last 10 years (continuous green line). The dotted green lines show the prediction error limits. This test checks how well does the model for the first 226 years data predict the last 10 years of data. The prediction is excellent. Credit: University of Helsinki


More information: Lauri Jetsu, Say Hello to Algol’s New Companion Candidates, The Astrophysical Journal (2021). DOI: 10.3847/1538-4357/ac1351


Provided by University of Helsinki

Researchers Identified Factors That Turn Normal Cells Into Liver Cancer Cells (Medicine)

Learning how to make cancer cells from normal cells provides mechanistic understanding about the early developmental stages of human cancer that can be used for preventing these tumorigenic mechanisms in the future.

Researchers at the University of Helsinki could show for the first time that normal human fibroblast cells can be converted to specific cancer cells using only factors that are commonly detected in actual human patients. Previous studies have achieved this only by using powerful viral factors that are not common in human cancers.

Since many human cancer types still lack specific diagnostic markers or effective targeted therapies, these mechanistic insights are important for developing novel diagnostic and treatment options.

Novel approach revealed cellular identity as a major determinant of how human cell transforms into a cancer cell

The research group of Professor Jussi Taipale that belongs to the Academy of Finland’s Center of Excellence in Tumor Genetics Research, developed a novel cellular transformation assay for studying the mutations that cause human cancer on a molecular level.

Using this novel assay, researchers were able to identify a minimal set of defined factors that can convert a normal human fibroblast cell to a liver cancer cell. They also discovered that cellular lineage and differentiation stage are critical factors that determine cell’s response to oncogenic mutations. This provides a mechanistic proof-of-principle for understanding why certain mutations cause cancer in particular tissues.

The study led by Dr. Biswajyoti Sahu was recently published in Oncogene.

“This is a first-of-its-kind study that introduced a novel approach to systematically investigate molecular determinants causing human cancers” says Dr. Sahu.

The innovative feature of the novel cellular transformation assay is to utilize cellular transdifferentiation, in which human fibroblast cells are converted to a different cell type using defined transcription factors, and to expose the cells to oncogenic factors during this transdifferentiation process.

“Since previous cancer genome sequencing studies have reported mutations in over 250 genes in different human tumor types, novel methods for studying their effects on tumorigenesis are highly warranted”, Dr. Sahu points out.

New openings for the development of diagnostics

Cancer can arise from various different human tissues. Although the common feature of all cancers is malignant growth caused by mutations in genes regulating critical cellular processes such as proliferation and apoptosis, same mutations do not cause cancer in all tissues. However, why a particular mutation causes cancer in some tissues but not in others is not well understood.

In this study, the authors identified the set of factors that can make normal cells to liver cancer cells by systematically studying different mutations that have previously been reported in human liver tumors.

”Our focus was on liver cancer, but importantly, similar approach can be used for studying various other human cancer types. Thus, this study can have a major impact on better understanding of tumorigenic mechanisms in the future” tells Professor Taipale.

Featured image: (Image: Mostphotos)


Original article: Biswajyoti Sahu, Päivi Pihlajamaa, Kaiyang Zhang, Kimmo Palin, Saija Ahonen, Alejandra Cervera, Ari Ristimäki, Lauri A. Aaltonen, Sampsa Hautaniemi, Jussi Taipale. Human cell transformation by combined lineage conversion and oncogene expression. Oncogene (2021). DOI: 10.1038/s41388-021-01940-0


Provided by University of Helsinki

Astronomers Make Most Distant Detection Yet of Fluorine in Star-forming Galaxy (Cosmology)

A new discovery is shedding light on how fluorine — an element found in our bones and teeth as fluoride — is forged in the Universe. Using the Atacama Large Millimeter/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, a team of astronomers have detected this element in a galaxy that is so far away its light has taken over 12 billion years to reach us. This is the first time fluorine has been spotted in such a distant star-forming galaxy.

We all know about fluorine because the toothpaste we use every day contains it in the form of fluoride,” says Maximilien Franco from the University of Hertfordshire in the UK, who led the new study, published today in Nature Astronomy. Like most elements around us, fluorine is created inside stars but, until now, we did not know exactly how this element was produced. “We did not even know which type of stars produced the majority of fluorine in the Universe!

Franco and his collaborators spotted fluorine (in the form of hydrogen fluoride) in the large clouds of gas of the distant galaxy NGP–190387, which we see as it was when the Universe was only 1.4 billion years old, about 10% of its current age. Since stars expel the elements they form in their cores as they reach the end of their lives, this detection implies that the stars that created fluorine must have lived and died quickly.

The team believes that Wolf–Rayet stars, very massive stars that live only a few million years, a blink of the eye in the Universe’s history, are the most likely production sites of fluorine. They are needed to explain the amounts of hydrogen fluoride the team spotted, they say. Wolf–Rayet stars had been suggested as possible sources of cosmic fluorine before, but astronomers did not know until now how important they were in producing this element in the early Universe.

We have shown that Wolf–Rayet stars, which are among the most massive stars known and can explode violently as they reach the end of their lives, help us, in a way, to maintain good dental health!” jokes Franco.

Besides these stars, other scenarios for how fluorine is produced and expelled have been put forward in the past. An example includes pulsations of giant, evolved stars with masses up to few times that of our Sun, called asymptotic giant branch stars. But the team believes these scenarios, some of which take billions of years to occur, might not fully explain the amount of fluorine in NGP–190387.

For this galaxy, it took just tens or hundreds of millions of years to have fluorine levels comparable to those found in stars in the Milky Way, which is 13.5 billion years old. This was a totally unexpected result,” says Chiaki Kobayashi, a professor at the University of Hertfordshire. “Our measurement adds a completely new constraint on the origin of fluorine, which has been studied for two decades.

The discovery in NGP–190387 marks one of the first detections of fluorine beyond the Milky Way and its neighbouring galaxies. Astronomers have previously spotted this element in distant quasars, bright objects powered by supermassive black holes at the centre of some galaxies. But never before had this element been observed in a star-forming galaxy so early in the history of the Universe.

The team’s detection of fluorine was a chance discovery made possible thanks to the use of space and ground-based observatories. NGP–190387, originally discovered with the European Space Agency’s Herschel Space Observatory and later observed with the Chile-based ALMA, is extraordinarily bright for its distance. The ALMA data confirmed that the exceptional luminosity of NGP–190387 was partly caused by another known massive galaxy, located between NGP–190387 and the Earth, very close to the line of sight. This massive galaxy amplified the light observed by Franco and his collaborators, enabling them to spot the faint radiation emitted billions of years ago by the fluorine in NGP–190387.

Future studies of NGP–190387 with the Extremely Large Telescope (ELT) — ESO’s new flagship project, under construction in Chile and set to start operations later this decade — could reveal further secrets about this galaxy. “ALMA is sensitive to radiation emitted by cold interstellar gas and dust,” says Chentao Yang, an ESO Fellow in Chile. “With the ELT, we will be able to observe NGP190387 through the direct light of stars, gaining crucial information on the stellar content of this galaxy.” 

More information

This research was presented in the paper “The ramp-up of interstellar medium enrichment at z > 4” to appear in Nature Astronomy (https://doi.org/10.1038/s41550-021-01515-9).


Provided by ESO

Physicists Observed 3 J/ψ Particles Emerging From A Single Collision Between Two Protons (Physics)

In a first for particle physics, the CMS collaboration has observed three J/ψ particles emerging from a single collision between two protons

It’s a triple treat. By sifting through data from particle collisions at the Large Hadron Collider (LHC), the CMS collaboration has seen not one, not two but three J/ψ particles emerging from a single collision between two protons. In addition to being a first for particle physics, the observation opens a new window into how quarks and gluons are distributed inside the proton.

The J/ψ particle is a special particle. It was the first particle containing a charm quark to be discovered, winning Burton Richter and Samuel Ting a Nobel prize in physics and helping to establish the quark model of composite particles called hadrons.

Experiments including ATLASCMS and LHCb at the LHC have previously seen one or two J/ψ particles coming out of a single particle collision, but never before have they seen the simultaneous production of three J/ψ particles – until the new CMS analysis.

The trick? Analysing the vast amount of high-energy proton–proton collisions collected by the CMS detector during the second run of the LHC, and looking for the transformation of the J/ψ particles into pairs of muons, the heavier cousins of the electrons.

From this analysis, the CMS team identified five instances of single proton–proton collision events in which three J/ψ particles were produced simultaneously. The result has a statistical significance of more than five standard deviations – the threshold used to claim the observation of a particle or process in particle physics.

These three-J/ψ events are very rare. To get an idea, one-J/ψ events and two-J/ψ events are about 3.7 million and 1800 times more common, respectively. “But they are well worth investigating,” says CMS physicist Stefanos Leontsinis, “A larger sample of three-J/ψ events, which the LHC should be able to collect in the future, should allow us to improve our understanding of the internal structure of protons at small scales.”

_____

Read more on the CMS website.

Featured image: A proton–proton collision event with six muons (red lines) produced in the decays of three J/ψ particles. (Image: CMS/CERN)


Provided by CERN

Researchers Reveal Relationship Between Li Abundance & Chromospheric Activity Indicator for Active Stars (Planetary Science)

In a study published in Astronomy & Astrophysics, Prof. XING Lifeng from Yunnan Observatories of the Chinese Academy of Sciences and his collaborators found the chromospheric activity index of a sample active stars increases with increasing lithium abundance.

Chromospherically active (CA) stars are a class of active stars characterized by strong chromosphere, transition region and coronal activity. Some of the objects are spectroscopically remarkable, showing evidence of very rapid rotation and that the Li I doublet at 670.8 nm. Whether a tight relation exists between the chromospheric activity and the lithium abundance in the chromospheric active late-type stars is still an open question. This relation can serve as a basis for the understanding of the relationship among activity, the light elements content and rotation of stars.

To investigate the correlation between the lithium abundance and the chromospheric activity for the chromospherically active late-type stars, the researchers selected a sample includes 14 active stars. These stars were selected from the cross-correlation of the ROSAT X-ray catalog and the Tycho catalog, and they are strong X-ray sources that have been identified as late-type stars. Spectroscopic observations for these sample stars were performed with the Coudé Echelle Spectrograph attached to the 1.8 m telescope at the Lijiang observatory of Yunnan Observatories.

Based on the high-resolution spectroscopic observations for the sample active stars, the researchers calculated the lithium abundance (on a scale where Log N(H) = 12.00) using the comparison of the measured Li I λ 670.8 nm equivalent width with curve of growth calculations in non-localthermodynamic-equilibrium conditions. The results showed that relationship between lithium abundance and the Ca II H & K emission index is that the activity of sample stars increases with increasing lithium abundance.

Moreover, the researchers found that the lithium abundance analogs progressively decrease as the rotation periods increase (rotation becomes slow) and the large values of the log R’HK go along with small values of Rossby numbers for the sample of chromospherically active stars.

The study indicates that the lithium abundance of 14 chromospherically active stars’ analogs progressively increases as the chromospheric activity index increases and/or the rotation periods decrease.


Reference

Lithium abundance in a sample of active stars: High-resolution spectrograph observation with the 1.8 m telescope


Provided by Chinese Academy of Sciences

Researchers Discover Special Eclipsing Dwarf Nova (Cosmology)

In a study published in The Astronomical Journal, Dr. HAN Zhongtao and Prof. QIAN Shengbang from Yunnan Observatories of the Chinese Academy of Sciences, Prof. Boonrucksar Soonthornthum from National Astronomical Research Institute of Thailand, and the collaborators, identified an eclipsing Z Cam-type dwarf nova, IPHAS J051814.34+294113.2 (IPHAS J0518). They found that IPHAS J0518 has a bimodal distribution of the outbursts, and that the complex behavior of accretion disk during outburst is a combined effect of the varying disc size and radial temperature gradient.Dwarf novae are a subtype of cataclysmic variables (CVs), and typically exhibit multiple optical outbursts. Z Cam-type stars are believed to share properties of both thermally unstable dwarf novae and thermally stable nova-like variables.

Eclipsing dwarf nova allows people to measure accurate parameters of the binary components and their orbital period changes, which is crucial for improving the understanding on CV evolution. The number of dwarf novae has been growing rapidly due to modern astronomical surveys. However, only a few eclipsing Z Cam stars have been known. The study of new eclipsing dwarf novae is important to test the theoretical models of the outburst.

The long-term light curves of IPHAS J0518 from Transiting Exoplanet Survey Satellite (TESS) and Zwicky Transient Facility (ZTF) telescope showed the alternation of long outbursts and short outbursts. Meanwhile, TESS data displayed two outbursts, as well as the striking eclipsing light curve.

Using the generalized Lomb-Scargle method and the weighted wavelet transform, the researchers obtained precise orbital period and the recurrence time of long and short outbursts.

By combining the derived outburst parameters and Large Sky Area Multi-Object Fiber Spectroscopy Telescope (LAMOST) spectra, the researchers discovered and identified IPHAS J0518 to be an eclipsing Z Cam-type dwarf nova. These data were also used to constrain the binary parameters.

Besides, the researchers analyzed the accretion disc eclipse and found that the total disc eclipse is possible during quiescence, whereas during outburst the disc would be only partially obscured. Further studies showed that the complex behavior of accretion disk during outburst appears more complicated than the single mechanism driven, and should be a combined effect of the varying disc size and radial temperature gradient.

The discovery of IPHAS J0518 is expected to reveal its disk structure and the brightness distribution, and allows people to trace the disk evolution with time during outburst.

Reference

TESS and ZTF Observations of an Eclipsing Z Cam-type Dwarf Nova IPHAS J051814.34+294113.2


Provided by Chinese Academy of Sciences