tag:blogger.com,1999:blog-11327257036733698232024-02-19T07:01:26.413-08:00Astronomy outreachBringing astronomy to the public, especially astronomy research in stars and planets. Written by professional astronomer Jorge Melendez, at the University of Sao Paulo, Brazil.Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-1132725703673369823.post-22961761874374171682015-01-20T03:07:00.000-08:002015-01-20T03:07:05.238-08:00Tips for observing with the HIRES echelle spectrograph at Keck (technical)The <a href="http://www2.keck.hawaii.edu/inst/hires/" target="_blank">HIRES</a> spectrograph at Keck is a grating cross-dispersed <a href="http://en.wikipedia.org/wiki/Echelle_grating" target="_blank">echelle</a> spectrograph. Albeit there is a lot of useful information on the <a href="http://www2.keck.hawaii.edu/inst/hires/" target="_blank">HIRES webpage</a>, here are a few more tips that may help you plan your observing run.<br />
<br />
If you are observing wavelengths above 6000 Å, one important concern is second order contamination. The HIRES spectrograph uses two <a href="http://en.wikipedia.org/wiki/Diffraction_grating" target="_blank">gratings</a> to disperse light, so that you can see fine details in the spectra. The main grating, the "<a href="http://en.wikipedia.org/wiki/Echelle_grating" target="_blank">echelle grating</a>", is a <a href="http://en.wikipedia.org/wiki/Diffraction_grating" target="_blank">diffraction grating</a> optimised for high spectral orders. Those high orders overlap, so you cannot distinguish them (they would fall at the same observing angle, i.e., at the same place in the detector). A second grating, which is perpendicular to the echelle grating, is used to disperse the echeller orders, so that they can fall at different regions on the detector. This second grating is the "cross disperser". Notice that a prism could be used instead as a cross disperser. For example, the MIKE spectrograph at the Magellan telescope uses a prism to disperse the echelle orders.<br />
<br />
When you are preparing your HIRES configuration, you must be careful about potential second order contamination (caused by the second grating -the cross disperser). "Second order" wavelengths below half of your maximum wavelength will contaminate your "first order" spectra. This doesn't happen with the MIKE spectrograph, because the cross disperser is a prism. You must worry about second order contamination with HIRES only if you are observing for lambda_1 (first order) > 6000 A. The reason is that for lambda_1 = 6000 A, the second order wavelength is half that value, lambda_2 = 3000 A (the ultraviolet atmospheric cutoff). So, Earth's atmosphere would be your "filter", blocking the second order light below 3000 A.<br />
<br />
In practical terms, you must define first your maximum wavelength and then use a filter to cut the second order contamination of wavelengths half of that maximum value. For example, if you would like to observe up to lambda_1 = 9000 A, then you must use a filter to block lambda_2 ≤ 4500 A. There are several filters available with HIRES, so that you can use the more convenient. For example, if you want to observe the OI triplet at 777 nm, then you may want to set up a maximum lambda_1 = 778m, corresponding to lambda_2 = 389 nm, and so you may choose the kv389 filter. Notice, however, that the filters are not perfectly sharp, so that there would be some small second order contamination around the OI triplet. This contamination is minor, so you may be OK with it. All depends on the level of extra "noise" that you're willing to accept. For the majority of observers aiming at low-moderate S/N (let's say, S/N ≤ 300), this should be OK. If you want to exclude any minor contamination to the OI triplet, then you must use a redder filter. In the example above, you would need a filter with lambda > 389nm. The problem is that if you use a filter that is too "red", then you may also block interesting regions of the first order light. For example, if you use a filter to block lambda < 400 nm, then you will miss the H and K lines.<br />
<br />
My favourite configuration with HIRES/red is to use the cross-disperser angle xdisp = +0.24, echelle angle = 0.0, and filter kv389. In this configuration the useful spectral coverage would be from about 390 - 780 nm, so you can get data from the H and K lines in the UV to the OI triplet at 777nm. The HIRES mosaic detector would actually cover a few more orders in the red, but they would be contaminated by second order light. So, my reddest useful order in this configuration would be the order of the OI triplet.<br />
<br />
Regarding the spectral resolution, you can achieve R ~ 90 000 - 95 000 with HIRES. This is based on my own measurements taken in 2004 - 2006. The highest resolution is achieved with the 0.4" slit, corresponding to about 2 pixels, so you MUST use 1x1 binning (i.e., no binning). For the highest resolution I recommend the E4 slit, that is long enough for sky subtraction. If you're using a slit ≥ 0,8 arc sec, then you can bin by two (2x2 binning) without loosing any spectral resolution.<br />
<br />Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-54640767954301423582014-11-12T16:28:00.004-08:002014-11-15T16:27:37.557-08:00Brazil: much more than soccer<div class="separator" style="clear: both; text-align: center;">
</div>
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjseJwHhX19wUQiG2PcAADOqxswOWs5bu6VmxT0YM73egyk4kOEIqfsE2t2VmrQq61Le6DRe86sEAL4TEPOqf0hZcPT-FO78OqD0vS78O6vX4ugS-hU8Xl7fEzhZ1-936KyyTTkM-duFIJ2/s1600/2014_11_flag.jpg" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"><img border="0" height="200" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjseJwHhX19wUQiG2PcAADOqxswOWs5bu6VmxT0YM73egyk4kOEIqfsE2t2VmrQq61Le6DRe86sEAL4TEPOqf0hZcPT-FO78OqD0vS78O6vX4ugS-hU8Xl7fEzhZ1-936KyyTTkM-duFIJ2/s200/2014_11_flag.jpg" width="195" /></a></div>
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: Arial, Helvetica, sans-serif; font-size: 12pt; font-weight: 600;">Encrypted in its flag lies one of the areas in
which the nation has a lot of potential:
Astronomy.</span><br />
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="color: #666666; font-family: 'Trebuchet MS', sans-serif; text-align: right;">by Viviana Peña Márquez, student of</span><span style="color: #666666; font-family: 'Trebuchet MS', sans-serif; text-align: right;"> <a href="http://www.astro.iag.usp.br/~jorge/aga421/" target="_blank">Astronomy Outreach</a> </span><span style="color: #666666; font-family: 'Trebuchet MS', sans-serif; text-align: right;">at IAG/USP</span><br />
<div class="page" title="Page 1">
<div class="section" style="background-color: rgb(100.000000%, 100.000000%, 100.000000%);">
<div class="layoutArea">
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: AvenirNext; font-size: 12pt;"><br /></span>
<span style="font-family: AvenirNext; font-size: 12pt;">When international media talk about Brazil, it is often about its soccer culture,
especially this year </span><span style="font-family: AvenirNext; font-size: 12pt;">because the country was the host of the World Cup 2014. But this
is also a nation that within the space of two decades has escalated 11 spots in the
world ranking of scientific production, reaching a decent 13th place worldwide,
according to a recent survey by Thomson Reuters Corporation published by the <a href="http://www1.folha.uol.com.br/ciencia/2014/11/1541834-em-20-anos-pais-vai-de-24-a-13-em-ranking-de-pesquisa.shtml" target="_blank"><i>Folha de São Paulo</i></a>.</span><br />
<div class="column">
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: AvenirNext; font-size: 12pt;"><br /></span>
<br />
<div class="page" title="Page 1">
<div class="section">
<div class="layoutArea">
<div class="column">
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: 'AvenirNext'; font-size: 12.000000pt;">Clearly, Brazil has more to brag about than just soccer. Encrypted in its flag lies one of
the areas in which the nation has a lot of potential: <b><a href="http://en.wikipedia.org/wiki/Astronomy" target="_blank">Astronomy</a></b>. To the surprise of
many, the position of the stars in the <a href="http://en.wikipedia.org/wiki/Flag_of_Brazil" target="_blank">Brazilian flag</a> are portrayed as they would be
seen by an imaginary observer at an infinite distance above Rio de Janeiro. But of
course, this is not the only bond the country has with the oldest science of all.
</span><br />
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: 'AvenirNext'; font-size: 12.000000pt;"><br /></span>
<span style="font-family: 'AvenirNext'; font-size: 12.000000pt;">In fact, </span><span style="font-family: AvenirNext; font-size: 16px;">this year, an international team led by astronomer Felipe Bragas-Ribas, of the Observatório Nacional at Rio de Janeiro, found for the first time </span><a href="http://www.eso.org/public/news/eso1410/" style="font-family: AvenirNext; font-size: 16px;" target="_blank">rings around an asteroid</a><span style="font-family: AvenirNext; font-size: 16px;">. The <a href="http://www.astronomy.com/issues/2014/january-2014" target="_blank">January 2014</a> issue of the Astronomy Magazine highlights the </span><span style="font-family: AvenirNext; font-size: 16px;">research on Black holes by</span><span style="font-family: AvenirNext; font-size: 16px;"> Brazilian astronomer Rodrigo Nemmen, as one of the top ten space stories of 2013. Last year, </span><span style="font-family: AvenirNext; font-size: 12pt;">Jorge Meléndez, an astronomer at the University of São Paulo, led a team that made a remarkable discovery: they found the </span><a href="http://www.eso.org/public/news/eso1337/" style="font-family: AvenirNext; font-size: 12pt;" target="_blank">oldest solar twin</a><span style="font-family: AvenirNext; font-size: 12pt;">. </span><span style="font-family: AvenirNext; font-size: 12pt;">These are examples of the impact
that Brazil is making in the international astronomy arena.</span><br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"></a></div>
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: left; float: left; margin-bottom: 1em; margin-right: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: 'AvenirNext'; font-size: 12.000000pt;"><br /></span>
<span style="font-family: 'AvenirNext'; font-size: 12.000000pt;">Speaking about twins and to get a better image about Brazil’s impact in astronomy,
let’s compare the Institute of Astronomy and Geophysics (<a href="http://www.iag.usp.br/" target="_blank">IAG</a>) at the <a href="http://en.wikipedia.org/wiki/University_of_S%C3%A3o_Paulo" target="_blank">University of São Paulo</a> and the Institute of Astronomy and Space Physics (<a href="http://www.iafe.uba.ar/" target="_blank">IAFE</a>) at the <a href="http://en.wikipedia.org/wiki/University_of_Buenos_Aires" target="_blank">University of Buenos Aires</a>. These institutes have about the same amount of Astronomy professors, belong to
the best universities in their respective countries and are located in the largest
metropolitan areas of South America. </span><span style="font-family: 'AvenirNext'; font-size: 12pt;">One way to make this comparison is through the <i>m-index</i>, a measure that shows the
impact </span><span style="font-family: AvenirNext; font-size: 12pt;">(</span><a href="http://en.wikipedia.org/wiki/H-index" style="font-family: AvenirNext; font-size: 12pt;" target="_blank"><i>h-index</i></a><span style="font-family: AvenirNext; font-size: 12pt;">) </span><span style="font-family: AvenirNext; font-size: 16px;">of the published work </span><span style="font-family: AvenirNext; font-size: 16px;">of a scientist </span><span style="font-family: AvenirNext; font-size: 12pt;">normalized by his or her experience (number of years publishing papers). This comparison (figure below) shows that both</span><span style="font-family: AvenirNext; font-size: 12pt;"> the IAG and the IAFE have very similar <i>m-index</i> impact,
indicating a similar competitiveness internationally.</span><br />
<span style="font-family: AvenirNext; font-size: 12pt;"><br /></span>
<br />
<div class="separator" style="clear: both; text-align: center;">
</div>
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjGZW0_POEGHOaC-AfZHdssHIhGScNd6dV4Ke8w4zieECj63GfArE71WDzOn8YK_qI2C77_aNhkZfJE07MB-I21RO7uSLud7TXlO94ESYLmh84Ee3CIb0VK4awkN2GLqsbztkQV2cuz92B/s1600/2014_11_iag_iafe.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" height="313" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgjGZW0_POEGHOaC-AfZHdssHIhGScNd6dV4Ke8w4zieECj63GfArE71WDzOn8YK_qI2C77_aNhkZfJE07MB-I21RO7uSLud7TXlO94ESYLmh84Ee3CIb0VK4awkN2GLqsbztkQV2cuz92B/s640/2014_11_iag_iafe.jpg" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-family: AvenirNext; font-weight: 600;">Comparison between the impact (</span><i style="font-family: AvenirNext; font-weight: 600;">m-index</i><span style="font-family: AvenirNext; font-weight: 600;">) of publications by astronomers at the Institute of Astronomy and Geophysics (IAG, Brazil) and the Institute of Astronomy and Space Physics (IAFE, Argentina). </span></td></tr>
</tbody></table>
<span style="font-family: AvenirNext; font-size: 12pt;"><br /></span></div>
</div>
</div>
</div>
<div class="page" title="Page 2">
<div class="section">
<div class="layoutArea">
<div class="column">
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: 'AvenirNext'; font-size: 12.000000pt;">Nevertheless, the nation needs to keep taking actions in order to achieve its full
potential. Meléndez’s discovery of the oldest known solar twin was possible because of the use of an
elite telescope that belongs to the European Southern Observatory (<a href="http://www.eso.org/public/" target="_blank">ESO</a>). Further
astounding discoveries by Brazilian astronomers could be made if the country
becomes ratified as a member of ESO, a process that started in 2010. </span><br />
<a href="https://www.blogger.com/blogger.g?blogID=1132725703673369823" imageanchor="1" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"></a><span style="font-family: AvenirNext; font-size: 12pt;"><br /></span>
<span style="font-family: AvenirNext; font-size: 12pt;">“There would be enormous benefits in different fronts. In the technological front, we
could have partnerships to develop instrumentation for ESO [...] Regarding the use of
the telescopes, we will be equal partners with other European countries, so that we
could compete for observing time either for small or large projects. This can allow
Brazilian astronomers to develop ambitious projects involving large allocations (about
50-100 nights) of observing time, something that is not possible in other
observatories where Brazil has only a small share of time. Currently I'm developing
one of those ‘Large ESO Programmes’, to search for planets around solar twins.” - says
Meléndez.</span><br />
<span style="font-family: 'AvenirNext'; font-size: 12.000000pt;"><br /></span></div>
</div>
</div>
</div>
<div class="page" title="Page 3">
<div class="section">
<div class="layoutArea">
<div class="column">
<span style="font-family: 'AvenirNext'; font-size: 12.000000pt;">In addition, Meléndez, who is also the astronomer with the highest <i>m-index</i> at the IAG Astronomy Department of the University of São Paulo, affirms that: “Brazil only invests about half of what developed
countries invest in science and technology, hence we need aggressive investments.”
</span><br />
<span style="font-family: 'AvenirNext'; font-size: 12.000000pt;"><br /></span>
<span style="font-family: 'AvenirNext'; font-size: 12.000000pt;">Perhaps the key to improve even more the impact of Brazil's astronomy is also
encrypted in its flag: </span><span style="font-family: 'AvenirNext'; font-size: 12.000000pt; font-style: italic;">Ordem e <b>Progresso (</b></span><span style="font-family: 'AvenirNext'; font-size: 12.000000pt;">Order and <b>Progress)</b>, a progress that could be achieved by making available to the Brazilian astronomical community the world's best telescopes to perform cutting-edge research.</span><br />
<span style="font-family: 'AvenirNext'; font-size: 12.000000pt;"><br /></span></div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-23956263410032283592014-11-02T15:07:00.000-08:002014-11-02T15:07:35.886-08:00Brazil lags behind developed countries in science funding<span style="font-family: Arial, Helvetica, sans-serif;"><b>Brazil is the <a href="http://en.wikipedia.org/wiki/Economy_of_Brazil" target="_blank">seventh largest economy</a> on Earth, but despite being an important player in the world, its expenditure in science is way behind developed countries.</b></span><br />
<br />
Below I show the science spending in different countries in 2011, using publicly available data from the <a href="http://data.worldbank.org/indicator/GB.XPD.RSDV.GD.ZS" target="_blank">worldbank</a>. As can be seen, Brazil expenditure in science is only about 1,2% of its <a href="http://en.wikipedia.org/wiki/List_of_countries_by_GDP_%28nominal%29" target="_blank">GDP</a> (gross domestic product). This is much lower than developed countries with lower GDP than Brazil, such as Austria (2.8%), Denmark (3%), Finland (3.8%) and Sweden (3.4%). If we compare Brazil with countries with higher GDP, science funding in the country is also below. For example, the USA (1st economy, 2.8%), China (2nd, 1.8%), Japan (3rd, 3.4%), Germany (4th, 2.9%), France (5th, 2.3%), and United Kingdom (6th, 1.8%).<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFTaiynOz896ifQv5OTjP7-XuTQyxlX7MLX64kGgZyXsj4UcTLm7U1UrfagHbsABE-t2u9Ync8ElzH4PF0HFaJAg88NtgqeiiabrQ4L9GplKUFb-00UNmL1RQ8OX856zYcAWKe9fYsEZQF/s1600/2014_11_gdp_percentage.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFTaiynOz896ifQv5OTjP7-XuTQyxlX7MLX64kGgZyXsj4UcTLm7U1UrfagHbsABE-t2u9Ync8ElzH4PF0HFaJAg88NtgqeiiabrQ4L9GplKUFb-00UNmL1RQ8OX856zYcAWKe9fYsEZQF/s1600/2014_11_gdp_percentage.jpg" height="257" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Science funding in percentage of the GDP, using data from the <a href="http://data.worldbank.org/indicator/GB.XPD.RSDV.GD.ZS" target="_blank">worldbank</a>. Brazil only invests 1,2% in science. (c) Jorge Meléndez</td></tr>
</tbody></table>
This low funding in science probably explains why the number of published scientific works in Brazil is only about half of what it should be for the size of its GDP, as shown in the figure below. The low number of papers simply means that Brazil is not investing enough in science, as already pointed out by the plot above.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEifaueprDJzcllbkA9sMXWgKKzY2cFyd1Gf9rl4HfvluUsjG2rjVXB7XhovFKNG_h8b64cqQQSs5a4FzZ8xmcZOW9ZlORxKkrIBzKtYfo9fMRsxaWEbfzBp4_amZ9Yals7_MrNHPVHk9AxW/s1600/2014_11_pib_papers_english.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEifaueprDJzcllbkA9sMXWgKKzY2cFyd1Gf9rl4HfvluUsjG2rjVXB7XhovFKNG_h8b64cqQQSs5a4FzZ8xmcZOW9ZlORxKkrIBzKtYfo9fMRsxaWEbfzBp4_amZ9Yals7_MrNHPVHk9AxW/s1600/2014_11_pib_papers_english.jpg" height="372" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">The number of papers published in Brazil is too low for the size of its economy. Figure made using data from the world bank and Thomson Reuters. (c) Jorge Meléndez.</td></tr>
</tbody></table>
Based on the comparisons above, I suggest that Brazil should increase its funding in science and technology by about a factor of two. In Astronomy, the obvious choice would be to invest in the European Southern Observatory (ESO), the world largest and more productive observatory on Earth, that will built the 39m ELT, the largest telescope on Earth.<br />
<br />Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-4583825105740644872014-10-24T20:53:00.003-07:002014-10-26T11:04:41.620-07:00Astronomy can help develop poor countriesWhy should a developing nation such as Brazil invest in Astronomy while there is still poverty in the country? Because Astronomy is key to fight poverty and improve lives.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEJiMnxpcWbmchnLrAn_8_ZoW8zOcFvQ7zfBwUrPf5EJ2PMvLNxsD3hkjGUtrPhvJk6K2V51jG9Zcyp_0wk7frcIhNRyPWYg8GtZygA51ZnyXwW6C6lq_HYdDriQLn4GF3ydM2vcWz0iXj/s1600/2014_10_human_poverty.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiEJiMnxpcWbmchnLrAn_8_ZoW8zOcFvQ7zfBwUrPf5EJ2PMvLNxsD3hkjGUtrPhvJk6K2V51jG9Zcyp_0wk7frcIhNRyPWYg8GtZygA51ZnyXwW6C6lq_HYdDriQLn4GF3ydM2vcWz0iXj/s1600/2014_10_human_poverty.jpg" height="253" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Countries that invest less in science have more human poverty. Figure by Jorge Meléndez based on worldmapper.org</td></tr>
</tbody></table>
<br />
Astronomy is THE interdisciplinary science per excellence. It is based on physics and maths, but it can also involve other areas such as chemistry, meteorology, geology, biology, history and archeology; it has also a strong technological component, as advanced technology is required to built large telescopes and state-of-the-art instrumentation. Astronomy can greatly contribute to improve education at different levels, helping students to interconnect apparently unrelated areas. More importantly, Astronomy fascinate children, being thus an excellent vehicle for introducing them to science and technology, which are fundamental to develop a country.<br />
<br />
Soccer is a national passion in Brazil, where soccer players are celebrities. It is OK to follow soccer as a career, but certainly a country needs other role models besides soccer players. We urgently need inspiring role models in science, we need successful scientists performing cutting-edge science. If we aspire to make major discoveries, we certainly need appropriate facilities. Brazilian astronomers were very excited back in 2010, when Brazil signed an agreement to join ESO, the largest and more productive observatory on Earth; unfortunately, Brazilian authorities are taking too long to ratify it.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYww0cMdgEISAJtrIcJ8HthCLHAQFDta-oLyeyhLr4XjLjWsP7aFzqklpP0BimXpGw7CMv3Uxsl_m0rnKjZWP3jFsU5N-igOjdFS9c5w0BREV953pi_7y6l6njsq0VqBgS3iHsLaVIm2ef/s1600/2014_10_Brazil_babak_tafreshi.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYww0cMdgEISAJtrIcJ8HthCLHAQFDta-oLyeyhLr4XjLjWsP7aFzqklpP0BimXpGw7CMv3Uxsl_m0rnKjZWP3jFsU5N-igOjdFS9c5w0BREV953pi_7y6l6njsq0VqBgS3iHsLaVIm2ef/s1600/2014_10_Brazil_babak_tafreshi.jpg" height="253" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="background-color: white; color: #262626; font-family: arial, helvetica, sans-serif; line-height: 16px; text-align: start;">The Southern sky as seen from Brazil. (c) Babak Tafreshi</span></td></tr>
</tbody></table>
An example of how astronomical discoveries can promote science in Brazil, was the <a href="http://www.eso.org/public/news/eso1337/" target="_blank">oldest solar twin identified</a> by an international team led by Brazilian astronomers in 2013. An important implication is that it helped to solve the lithium mystery in the Sun. The news was highlighted both internationally and nationally, with more than 100 local media reporting the discovery. A local competition made to "name" the oldest solar twin, received almost one thousand entries, showing thus an important impact. Other recent exciting finding by Brazilian astronomers was the discovery of <a href="http://www.eso.org/public/news/eso1410/" target="_blank">rings around an asteroid</a>, known previously only around giant planets. Another example by a developing country is the recent successful Indian space mission to Mars, showing how great science achievements can be a matter of national pride.<br />
<br />
Brazil's exports are mainly primary mineral and agricultural products. We need more than just exporting <a href="http://en.wikipedia.org/wiki/Coffee_production_in_Brazil" target="_blank">coffee</a> and <a href="http://en.wikipedia.org/wiki/Banana_production_in_Brazil" target="_blank">bananas</a> to develop a country. The development of technology in Brazil is way behind other countries; most high tech products are either imported or just assembled here. We need to invest heavily in education, science and technology, and Astronomy can help to educate our children, and stimulate our most talented minds to follow careers in science and technology.<br />
<br />Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-90610301279180376682014-10-19T15:44:00.000-07:002014-10-20T05:03:19.910-07:00New simulations explain why Mars is so small<br />
<div class="page" title="Page 1">
<div class="section">
<div class="layoutArea">
<h3 style="text-align: right;">
<span style="font-family: Trebuchet MS, sans-serif; font-size: small;"><span style="font-weight: normal;">Press release IAG/2014-02, Embargoed until 2014 February 20 at 13:00 UT</span></span></h3>
<h3 style="text-align: right;">
<span style="font-family: Trebuchet MS, sans-serif;"><span style="color: #666666; font-size: x-small; font-weight: normal;">Press-release </span><span style="color: #666666; font-size: x-small; font-weight: normal;">example</span><span style="color: #666666; font-size: x-small; font-weight: normal;"> </span><span style="color: #666666; font-size: x-small; font-weight: normal;">by Viviana Peña Márquez, student of</span><span style="color: #666666; font-size: x-small; font-weight: normal;"> </span><i style="color: #666666; font-size: small; font-weight: normal;">Divulgação em Astronomia</i><span style="color: #666666; font-size: x-small; font-weight: normal;"> </span><span style="color: #666666; font-size: x-small; font-weight: normal;">at IAG/USP</span></span></h3>
<h3 style="text-align: left;">
<span style="font-size: small; font-weight: normal;"><i><span style="font-family: Trebuchet MS, sans-serif;"><br /></span></i></span></h3>
<h3 style="text-align: left;">
<span style="font-size: large; font-weight: normal;"><i><span style="font-family: Trebuchet MS, sans-serif;">Astronomers present model to help solve Mars’ size mystery</span></i><span style="font-family: Helvetica Neue, Arial, Helvetica, sans-serif;"> </span></span></h3>
<div class="column">
<div class="page" title="Page 1">
<div class="section" style="background-color: rgb(100.000000%, 100.000000%, 100.000000%);">
<div class="layoutArea">
<div class="column">
<span style="font-family: AvenirNext;"><span style="font-size: 13pt; font-weight: 600;"><br /></span></span>
<span style="font-family: AvenirNext;"><span style="font-size: 13pt; font-weight: 600;">Existent planet formation theories have successfully explained why there are
jovian and terrestrial planets in our solar system, but have failed to justify why
the Red Planet is so small. According to most models, Mars should be as big as
Venus and Earth, but the planet is only a tenth of its </span><span style="font-size: 17px; font-weight: 600;">neighbours</span><span style="font-size: 13pt; font-weight: 600;"> Through
new simulations, an international team led by Brazilian astronomer André
Izidoro, shed light on the mystery of why Mars failed to grow similar in size.</span></span><br />
<br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">Previous simulations of planet formation, with a solar nebula that varies smoothly with
distance from the Sun, produce a body with approximately the size of our own
planet Earth in the orbit of Mars, i.e. 1.5 AU* from the Sun. A puzzling matter
since the four rocky planets are composed by the same planetary embryos.
</span><br />
<br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">Following studies showed that a planet with the size of Mars could have
formed in its orbit if the solar nebula was nonuniform, with a belt containing
more material near today’s Earth, followed by a belt with less material in the
region where the Red Planet is today.
</span><br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;"><br /></span>
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjBqwvXDXuvALoL_ErFBCvIxpg5JrqRiLWZYIhhyCp9ZVQMYD6aKdIc75sxc7SqEjpL96UW_3rTda5_qP-MwE16dhPmNt4KX0E6lELZho77QIoR97nAgZinTQHj7k3Qgmekq7dMSZsMMhCV/s1600/2014_10_grand_tack_izidoro.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjBqwvXDXuvALoL_ErFBCvIxpg5JrqRiLWZYIhhyCp9ZVQMYD6aKdIc75sxc7SqEjpL96UW_3rTda5_qP-MwE16dhPmNt4KX0E6lELZho77QIoR97nAgZinTQHj7k3Qgmekq7dMSZsMMhCV/s1600/2014_10_grand_tack_izidoro.jpg" height="329" width="640" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;"><span style="font-family: AvenirNext; font-size: 15px; font-style: italic; text-align: start;">Contrast between “Grand Tack” model (B) and Izidoro’s model (A). </span><span style="font-family: AvenirNext; font-size: 15px; text-align: start;">(c) Science</span></td></tr>
</tbody></table>
<br /></div>
</div>
</div>
</div>
<div class="page" title="Page 2">
<div class="section" style="background-color: rgb(100.000000%, 100.000000%, 100.000000%);">
<div class="layoutArea">
<div class="column">
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">Up to now, the most valid theory to explain such unusual distribution is called
the “Grand Tack” model, that assumes the inward and then outward migration of Jupiter. These unlikely events in the
early Solar System could have created favorable conditions for the formation of a
planet such as Mars.</span><br />
<span style="font-family: AvenirNext;"><span style="font-size: 17px;"><br /></span></span>
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">Looking for a better alternative to the “Grand Tack” model, Izidoro and his team
assumed that material flowed toward the Sun moving at different speeds at
different distances from the star, generating a depletion of material somewhere
between 1 AU and 3 AU. A gap that could explain Mars’ size. </span><span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">“This deficit in local mass may be common in protoplanetary disks. However,
the location and characteristics of this region can be very sensitive to the
properties of each model. In our case, Mars formation around 1.5 AU is also
due to the gravitational effects exerted by Jupiter and Saturn,” explains Izidoro. </span><br />
<span style="font-family: AvenirNext;"><span style="font-size: 17px;"><br /></span></span>
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">Othon Winter, researcher of the UNESP Orbital Dynamics and Planetology Group,
concludes: “The model is quite complete because, besides giving an
explanation to the mystery of the size of the Red Planet, it also maintains and
manages to generate the other terrestrial planets in their current orbits and
masses.”
</span><br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;"><br /></span>
</div>
</div>
</div>
</div>
<br />
<div class="page" title="Page 3">
<div class="section" style="background-color: rgb(100.000000%, 100.000000%, 100.000000%);">
<div class="layoutArea">
<div class="column">
<span style="color: rgb(28.519990%, 60.786810%, 78.972140%); font-family: 'AvenirNext'; font-size: 13.000000pt;">MORE INFORMATION</span><br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">This research was presented in the paper “Terrestrial planet
formation in a protoplanetary disk with a local mass depletion: A successful
scenario for the formation of Mars”, by André Izidoro et al. </span><span style="font-family: AvenirNext; font-size: 17px;">to appear in</span><span style="font-family: AvenirNext; font-size: 13pt;"> the </span><span style="font-family: AvenirNext; font-size: 13pt; font-style: italic;">Astrophysical
Journal Letters </span><span style="font-family: AvenirNext; font-size: 13pt;">(February 2014</span><span style="font-family: AvenirNext; font-size: 13pt;">).</span><br />
<span style="font-family: AvenirNext;"><span style="font-size: 17px;"><br /></span></span>
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">The team is composed of André Izidoro (Universidade Estadual Paulista, Brazil
[UNESP] - University of Nice-Sofia, France), Nader Haghighipour (University of
Hawaii-Manoa, USA), Othon Winter (UNESP), and Masayoshi Tsuchida (UNESP). </span><br />
<span style="font-family: 'Helvetica'; font-size: 25.000000pt;"><br />
</span><span style="color: rgb(28.519990%, 60.786810%, 78.972140%); font-family: 'AvenirNext'; font-size: 13.000000pt;">LINKS</span><span style="font-family: 'AvenirNext'; font-size: 13.000000pt;"><br /></span><br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">• <a href="http://adsabs.harvard.edu/abs/2014ApJ...782...31I" target="_blank">Research Paper</a></span><br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;"><br />
</span><span style="color: #499bca; font-family: AvenirNext; font-size: 13pt;">NOTES</span><span style="font-family: AvenirNext; font-size: 13pt;"><br /></span><br />
<span style="font-family: AvenirNext; font-size: 13pt;">* One astronomical unit (AU) is the distance from the Earth to the Sun.</span><br />
<span style="font-family: AvenirNext; font-size: 13pt;"><br /></span>
<br />
<span style="color: rgb(28.519990%, 60.786810%, 78.972140%); font-family: 'AvenirNext'; font-size: 13.000000pt;">CONTACT</span><br />
<span style="font-family: 'AvenirNext'; font-size: 13.000000pt;">André Izidoro<br />
University of Nice-Sophia, Nice, France.<br />
Phone: xx x xxxx xxxx<br />
E-mail: xxxxxxx@xxxxx.xxxx.xx</span></div>
</div>
</div>
</div>
</div>
</div>
</div>
</div>
Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-44038253774831682742014-10-15T21:29:00.000-07:002014-10-16T09:06:53.638-07:00From the Peruvian Andes to galaxies and the Big BangA century ago our universe was just a little village called the Milky Way. Today, we know that there are billions of galaxies in the cosmos, and that the universe is expanding due to the Big Bang. The Peruvian Andes played a fundamental role in those discoveries.<br />
<br />
Less than a century ago, <a href="http://en.wikipedia.org/wiki/Edwin_Hubble" target="_blank">Edwin Hubble</a> showed that certain "nebulae" are actually galaxies like our Milky Way, by using the so-called period-luminosity relationship of variable stars known as <a href="http://en.wikipedia.org/wiki/Cepheid_variable" target="_blank">cepheids</a>, that allowed him to estimate distances. Using cepheids located in the Andromeda "nebula", Hubble concluded in the 1920s that Andromeda is far outside our Galaxy. Later, Hubble found that the most distant galaxies have the largest velocities away from Earth. This means that the Universe is expanding, and that everything started in the Big Bang.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMXl-1pO3HJoz4jtxS6QG_Jmk3yyNx3HgLZx7r4-FtDlBZSXm5v-D6ZV8qCBR3qGdDh-LXi3tazDGRJnOUllg14JRq5F2T0-Sv9qqZYuXI6Pg8dzHP_Gp9sKcyWeJ-GqyXVG19oZjHAx_O/s1600/andromeda.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhMXl-1pO3HJoz4jtxS6QG_Jmk3yyNx3HgLZx7r4-FtDlBZSXm5v-D6ZV8qCBR3qGdDh-LXi3tazDGRJnOUllg14JRq5F2T0-Sv9qqZYuXI6Pg8dzHP_Gp9sKcyWeJ-GqyXVG19oZjHAx_O/s1600/andromeda.jpg" height="160" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Andromeda "nebula". (c) NASA.</td></tr>
</tbody></table>
Hubble relied on the period-luminosity relationship of cepheids to estimate how far away are distant galaxies. This relationship was discovered by American astronomer <a href="http://en.wikipedia.org/wiki/Henrietta_Swan_Leavitt" target="_blank">Henrietta Leavitt</a>, using observations taken in the Peruvian Andes, more exactly from the <a href="http://ocp.hul.harvard.edu/expeditions/boyden.html" target="_blank">Boyden Station in Arequipa</a>. The Harvard College Observatory built that observatory in the 1890s and early 1900s, to have access to the Souther Sky. Henrietta Leavitt measured the brightness of variable stars in the Magellanic Clouds, and discovered the period-luminosity relationship followed by cepheid variables.<br />
<br />
Thus, observations from the Peruvian Andes were key to set the standard ruler to measure large distances, leading to the birth of Extragalactic Astronomy and Cosmology. In another post I'll describe how observations gathered in Harvard's observatory in Arequipa led to the birth of Stellar Astrophysics.Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-18870102436050705252014-10-12T13:46:00.000-07:002014-10-13T12:48:04.917-07:00Stellar populations. I) What is the difference between population and sample?How many stars are in the Milky Way? The total <b>population</b> of stars in our Galaxy is enormous (about a few hundred billion). We cannot count or study every single star in our Galaxy, hence Astronomers must select relatively small <b>samples</b> of stars (hundreds or thousands) to study our Galaxy.<br />
<br />
<table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="clear: left; margin-bottom: 1em; margin-left: auto; margin-right: auto; text-align: center;"><tbody>
<tr><td style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_uVQ07kYmSUXe5kx-_WilbT1XHS6o4CVNexwEukvYxyYY7TE4KFFfkbxonuu_0LUbNzZL1EsiioxDHI48WG_JGWvP50DEOXCurL_JtL3mJRmuIaCMEK2Zckvl2Hr3xKwD5DNUzuZ0WwPp/s1600/eso_gerd_huedepohl_7.jpg" imageanchor="1" style="margin-left: auto; margin-right: auto;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_uVQ07kYmSUXe5kx-_WilbT1XHS6o4CVNexwEukvYxyYY7TE4KFFfkbxonuu_0LUbNzZL1EsiioxDHI48WG_JGWvP50DEOXCurL_JtL3mJRmuIaCMEK2Zckvl2Hr3xKwD5DNUzuZ0WwPp/s1600/eso_gerd_huedepohl_7.jpg" height="162" width="400" /></a></td></tr>
<tr><td class="tr-caption" style="text-align: center;">Milky Way as seen from Paranal. <a href="http://www.eso.org/public/archives/images/medium/gerd_huedepohl_7.jpg" target="_blank">(c) ESO</a></td></tr>
</tbody></table>
How to select a <b>sample</b> that is representative of a large <b>population</b>? This is far from trivial; incorrect conclusions can be obtained if there is a bias in the selection. An example is the study of <b>the mean age of the whole population of stars in our Galaxy</b>. Imagine that to do this job you select a <b>sample of stars located in the Galactic halo, far away from the Galactic disk</b>. Halo stars are old (about 10 Gyr), therefore you would incorrectly conclude that stars in our Galaxy are mostly old.<br />
<br />
Problems with sample selection can also affect our daily life. Think about polls for a Presidential election, like the one we're having in Brazil. Poll companies cannot interview the <b>population of all Brazilian voters</b>, they have to select a <b>sample</b> that is not necessarily representative of the entire <b>population</b>. Indeed, the results of the first round were surprising, candidate Aécio Neves was the runner-up, gathering far more votes than those estimated from the polls. He will face current President Dilma in a second round, on October 26, 2014.<br />
<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
</div>
Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-5537491620371284292014-10-06T18:57:00.001-07:002014-10-06T18:57:28.852-07:0018 Sco, a solar twin rich in "technological" heavy elementsIf there are hypothetical planets around the solar twin 18 Sco, they should be rich in heavy elements such as silver, neodymium, dysprosium and europium. Here on Earth, many of those heavy elements are like "gold", because they are precious ingredients for some electronics. If there are habitable planets around 18 Sco, their civilisations will not lack these precious elements important in today's technology. 18 Sco is also rich in refractory elements, that are elements that in the early solar system easily formed dust, later planetesimals, and finally larger rocky objects such as Earth. Technical details on how the chemical abundances were obtained are given in <a href="http://adsabs.harvard.edu/abs/2014ApJ...791...14M" target="_blank">Meléndez et al. (2014)</a>.<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjvSJlGpTlBmZIujGSHpzScef7ursd_olWT-uv75Vg-LOlcYJiVqnsepKAnZcbXU56dGR7m3pwFR6TzICZJTZnEtDoUgoXgJNTVlRphOdL3ur_nZ09JUQijYa7LhcxaFSP-72G2mXSiXTXO/s1600/2014_10_18sco_heavy.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjvSJlGpTlBmZIujGSHpzScef7ursd_olWT-uv75Vg-LOlcYJiVqnsepKAnZcbXU56dGR7m3pwFR6TzICZJTZnEtDoUgoXgJNTVlRphOdL3ur_nZ09JUQijYa7LhcxaFSP-72G2mXSiXTXO/s1600/2014_10_18sco_heavy.jpg" height="404" width="640" /></a></div>
<br />Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0tag:blogger.com,1999:blog-1132725703673369823.post-84611584750539253062014-10-06T14:10:00.001-07:002014-10-06T14:10:17.225-07:00What is a solar twin?Depending on how stars resemble the Sun, astronomers refer to them as "solar type" stars, "solar analogs" and "solar twins". Solar twins are the the most similar to the Sun.<br />
<br />
A <b>solar type</b> star actually belongs to a broad category. Back in the XIX century, Father Angelo Secchi (1868, <i>Sugli Spettri Prismatici Delle Stelle Fisse</i>) observed bright stars using a spectrograph (an instrument that splits the light with such a power than besides the colours we can see lines from different chemical elements) and found that yellow stars showed a spectrum similar to the Sun's, hence called them <i>tipo solare.</i> The similarity was due to the limitations of early spectrographs. Work performed later divided those yellow stars actually in 3 different types, F, G (like the Sun) and K stars <a href="http://en.wikipedia.org/wiki/Stellar_classification" target="_blank">(see more about Stellar classification here)</a>, More specifically, solar type stars include stars from late F (the coolest F stars), G (like our Sun) and early K (the hottest K stars).<br />
<br />
A <b>solar analog</b> is more similar to the Sun, yet with important variations, such as differences in temperatures of up to 250 degrees in relation to the Sun, and with a chemical composition within a factor of 2 - 3 of the Sun's.<br />
<br />
<b>Solar twins</b> are stars nearly identical to the Sun in all their properties (such as mass, temperature, chemical composition). For example, it has been suggested that solar twins should have temperatures within 100 degrees and chemical composition within 25% of the Sun (<a href="http://adsabs.harvard.edu/abs/2009A%26A...508L..17R" target="_blank">Ramírez 2009</a>). The first star recognised as a solar twin was <a href="http://adsabs.harvard.edu/abs/1997ApJ...482L..89P" target="_blank">18 Sco</a>. This is the brightest solar twin, yet it is barely visible to the naked eye. The star that most approaches the concept of solar twin is <a href="http://adsabs.harvard.edu/abs/2012A%26A...543A..29M" target="_blank">HIP 56948</a>, also known as <a href="http://tierneylab.blogs.nytimes.com/2007/12/17/the-suns-long-lost-twin-gets-a-name-or-two/" target="_blank">Intipa Awachan</a>. Since stars of the same mass and chemical composition evolve in the same way, astronomers also call solar twins those stars with about the Sun's mass and composition. Hence, solar twins evolve as the Sun. Solar twins of different ages gives us the fascinating possibility of studying the past and future of the Sun. The oldest known solar twin is <a href="http://adsabs.harvard.edu/abs/2013ApJ...774L..32M" target="_blank">HIP 102152</a>.Prof. Dr. Jorge Meléndezhttp://www.blogger.com/profile/03024642939665978926noreply@blogger.com0