The Dance of Variable Stars: TESS Insights

Variable stars are celestial bodies that complete their cycles of brightness over time. Some brighten and dim in an orderly way, while others may be more chaotic. With the rise of new technologies, we have more data than ever to help us understand these stellar performers. One such technology is the Transiting Exoplanet Survey Satellite (TESS), which has been busy spotting stars that change brightness. In this article, we will explore how scientists classify these periodic variable stars and what that means for our understanding of the universe.

#The Rise of TESS

TESS is like a big flashlight in space, scanning vast stretches of the night sky for stars that twinkle and dance. Launched to find new planets, TESS has also turned out to be an excellent friend to astronomers interested in variable stars. In recent years, the number of these stars has shot up, thanks to TESS's ability to detect even the faintest changes in brightness. So, grab your telescope, because things are about to get interesting!

#Discovering Periodic Variable Stars

Using data collected from the first 67 sectors of TESS, scientists have identified a whopping 72,505 periodic variable stars. These stars come in all shapes and sizes, and we can group them into 12 unique categories. This classification includes familiar names like Cepheid stars and RR Lyrae Stars, as well as lesser-known types like GCAS and ROT stars.

To make sure we are doing a good job with classification, scientists consider various factors such as the period of brightness change, physical characteristics of the stars, and the shape of their light curves (the pattern of brightness over time). By using a machine learning tool called the random forest method, they can sort these stars based on 19 different parameters.

#Why Classify Variable Stars?

You might be wondering why we bother classifying stars at all. Well, each type of variable star tells us a different story about the cosmos. For example, Classical Cepheids are vital for measuring distances in space. They follow a consistent pattern that allows astronomers to calculate how far away they are. Similarly, RR Lyrae stars serve as distance indicators for globular clusters in our galaxy. Knowing the types of variable stars helps researchers piece together the structure of the Milky Way and beyond.

#TESS Data and Methodology

TESS gathers its data through a unique method. It uses four wide-field optical cameras to take pictures of the sky in segments known as sectors. Each sector measures the brightness of selected stars every two minutes. Over time, this data helps scientists track how these stars change in brightness, sometimes revealing periodic patterns.

To identify periodic variable stars, the researchers first organize all the data into two groups: those observed in only one sector and those seen in multiple sectors. They then analyze the light curves, looking for patterns that indicate a star's brightness is changing in a regular way, like clockwork.

#Period Finding and Noise

Finding the periods of these stars can be tricky business. Some stars have long periods, and if they weren’t observed long enough, it could lead to incorrect conclusions. To manage this, researchers impose limits on what they consider when measuring periods. This process helps to ensure a more accurate classification. Noise, or random fluctuations that can imitate periodic changes, is also a challenge. By simulating noise in the data, scientists can identify patterns that are genuinely periodic versus those that are just random blips.

#The Training Set

To classify the stars accurately, researchers need a training set of known variable stars. They cross-check with existing databases to build a solid base for their classifier. By comparing their findings with recognized catalogs, scientists ensure their classification is reliable. It’s like having a cheat sheet for a big exam!

#The Results

After going through all the data and classifications, researchers discover many new variable stars. Out of the 72,505 stars identified, 63,106 are classified for the first time, meaning they were not recognized in previous catalogs. This includes well-known types like Cepheids and Eclipsing Binaries, as well as some newly classified stars that nobody was even aware of before.

#Types of Periodic Variable Stars

Now let’s dive into the various categories of periodic variable stars. Each category has unique characteristics that help astronomers understand their roles in the universe.

#Classical Cepheids

Classical Cepheids are like the stars in a cosmic beauty pageant. They are bright, colorful, and show clear patterns in their brightness. These stars swell and shrink in size over a set period, creating a predictable change in brightness. Astronomers use them to measure distances in the universe, making them some of the most important stars in the sky.

#RR Lyrae Stars

These stars are shorter in period than Cepheids and are useful for tracking the ages and chemical compositions of old stars. RR Lyrae stars are often found in globular clusters, which are dense groups of stars that orbit galaxies. They are like the wise grandpas of the universe, helping us learn about the history of star formation.

#Eclipsing Binaries

Eclipsing binaries are a couple of stars that dance around each other, blocking each other's light from time to time. This type of variable star is vital for measuring stellar masses and radii. Because they can be observed from any angle, they provide very accurate information about their properties.

#Delta Scuti Stars

These stars are like the "in-between" stars. They have short periods and come in a variety of masses. Delta Scuti stars can help astronomers understand the processes that affect stars during their evolution. They put on quite a show with their small but noticeable flickers of brightness.

#Rotational Variables

Rotational variable stars are those that vary in brightness because of their rotation. Some of these stars have spots on their surfaces, similar to how our sun has sunspots. As these stars spin, their brightness changes depending on where the spots are located. It’s like a cosmic game of peek-a-boo!

#Young Stellar Objects

These are the baby stars in the universe. They are still in the process of forming and often show irregular brightness changes. Studying young stellar objects helps astronomers grasp how stars form and evolve. They’re the future of star power!

#The Importance of Classification

Categorizing periodic variable stars is not just an exercise in celestial bureaucracy; it provides essential insights into how stars evolve and fit into the larger universe. By documenting and classifying these stars, researchers gather information about the structure of the Milky Way, stellar evolution, and even the history of the cosmos.

#Consistency with Other Catalogs

Part of validating the discovery and classification of new stars involves comparing findings with existing catalogs, such as those from GAIA and ZTF. The consistency across these databases is crucial to building a complete picture. A high level of agreement means that researchers can be more confident in their classifications—reducing the number of "oops" moments, which we all want in science.

#Future Prospects

As TESS continues to gather data, we can expect to see more variable stars being discovered and classified. The future looks bright—literally! With more sectors observed and better methodologies, scientists will uncover even more about these twinkling wonders of the universe.

#Conclusion

In summary, the classification of periodic variable stars using data from TESS is an exciting frontier in astronomy. By refining our understanding of these stars, we gain insights into the broader universe. From helping us measure distances to understanding stellar evolution, periodic variable stars play a vital role in our cosmic knowledge. So, next time you gaze up at the night sky, remember the stars are not just shining; they are telling us their stories!