Radio Galaxy Zoo Talk

Radio Stars

  • JeanTate by JeanTate

    A1001 recently wrote about the ARG field ARG00002po in a Talk Discussion thread, ARG00002po star galaxy radio source?. From some preliminary analysis, it seems that the apparent host, SDSS J091926.58+614954.0, may be a star. If so, it would be an unusual object, a radio star.

    But what is a radio star? Have we volunteers found others here in RGZ? What have astronomers learned about them? What's the latest news about them? In this thread I hope we will explore these, and related, questions.

    Posted

  • JeanTate by JeanTate

    The first question - what is a radio star? - is very easy to answer, in principle.

    It is a star (as we usually understand that word) which emits electromagnetic radiation in the radio part of the spectrum.

    Our own Sun is a radio star, a fact discovered very early in the history of radio astronomy, in 1942 by James Hey {source}. A highly variable one too; solar flares are associated with some pretty strong radio emission, but when the Sun is "quiet", it is a pretty very radio source.

    If the Sun were at a distance of 1 parsec (pc), say, or 1,000 pc (a kilo-parsec, kpc), would we be able to detect its radio emissions? When flaring, at the former distance yes; even when flaring, at the latter distance no.

    The two main components of the Alpha Centauri system are stars somewhat similar to our own Sun. They were recently observed by the Australian Telescope Compact Array at 2 GHz and 17 GHz, and both were detected {words about S/how faint}:

    width:400

    Source: ATNF Daily Astronomy Picture 17 April 2018

    In one sense, a radio star is a star (in our own Milky Way galaxy) which has been observed to be a radio source, by a radio telescope (possibly in space, but mostly here on Earth).

    Note: I intend to update this, and other posts by me in this thread (except the first), with details (and corrections) as I learn of/find them.

    Posted

  • JeanTate by JeanTate

    Have we volunteers found any radio stars, here in RGZ?

    The quick answer: yes.

    A better answer: it's ... complicated.

    Even a cursory look through the Object Comments will quickly turn up dozens of radio sources which ~coincide with what look like point sources in WISE, and which the SDSS photometric pipeline classes as STAR (I have a Collection of these, {detail}).

    However, most if not almost all only appear to be stars (point sources); they are very likely quasars (QSOs).

    If there's an SDSS (or other) spectrum of these point sources, and if that spectrum shows that the object resembles a star in our Milky Way (MW) galaxy, it may get the hashtag #specstar (of course, many such objects will not have such a hashtag, if only because many of the volunteers hard at work classifying radio sources do not write Comments, and even among those who do, many surely do not know of that hashtag even if they found that the SDSS spectrum of the host is that of a MW star).

    So far, it seems there are ~a couple of dozen specstars. Here they are, along with the handle of the volunteer who first wrote about the ARG field or the apparent host, and when (in no particular order):

    ARG0000xj8: Dolorous_Edd, July 14 2017 11:08 AM

    ARG0001lwh: antikodon April 20 2016 10:47 AM. Also discussed in the thread ARG0001lwh: #specstar?

    ARG00009k4: Dolorous_Edd September 15 2017 9:07 AM

    ARG0002m7n: Dolorous_Edd July 16 2017 1:52 PM. But as HAndernach notes, this is actually a QSO (the SDSS spectroscopic pipeline's automatic classification is wrong)

    ARG0001z2q: Dolorous_Edd September 20 2017 8:51 AM

    ARG0002890: Dolorous_Edd June 28 2017 2:34 AM

    ARG0000enk: Dolorous_Edd October 15 2016 4:47 AM

    ARG0001tz1: JeanTate March 5 2018 1:25 PM

    ARG00003n0: Dolorous_Edd January 31 2017 8:16 AM

    ARG0001srz: 958bacsal July 7 2016 2:09 PM

    ARG0001qa5: JeanTate March 19 2017 4:38 PM

    ARG0000tnc: Dolorous_Edd July 10 2017 5:31 PM

    ARG0003c66: sisifolibre September 15 2017 7:42 PM

    ARG0002ux7: Dolorous_Edd September 20 2016 4:18 PM

    ARG00015wa: A1001 May 21 2017 2:41 PM

    ARG00009mw: Dolorous_Edd September 18 2016 4:38 PM

    ARG000167s: Dolorous_Edd March 30 2016 10:55 AM

    ARG0003f5x: JeanTate May 5 2018 9:37 AM

    Note: I intend to update this, and other posts by me in this thread (except the first), with details (and corrections) as I learn of/find them. In particular, I will add the SDSS ID, and the specclass of the candidate radio star.

    Posted

  • JeanTate by JeanTate

    What have astronomers learned about radio stars?

    This section would not have been possible without the inputs and advice from RGZ Scientists HAndernach and ivywong (private communications). A very big Thank You! 😃 Things that I've gotten right are mostly due to them; things wrong are on me.

    Wikipedia's Radio star is a brief if rather incomplete summary.

    Matthews (2014) "Radio Stars and their Lives in the Galaxy" is a good overview of what was then the state-of-play on this topic. It is not behind a paywall, so clicking on the ADS "Full Referred Journal Article" link will give you a PDF which you can download. The first sentence says it all:

    Radio emission has now been detected from stars across the entire Hertzsprung-Russell (H-R) diagram, spanning virtually every stage of stellar evolution.

    Here's my summary of where things stood, in late 2012, based mostly on Matthews (2014):

    Pre-Main Sequence stars (Young Stellar Objects, YSOs): more mystery than established astrophysics. Magnetic fields likely play a key role (as in all radio stars), but it is not yet known what (mostly cm) radio emission is thermal vs non-thermal. And the GĂźdel-Benz relation (more later) between radio and x-ray emission does not seem to hold. YSO jets may produce double lobes, perhaps even very rare double-lobed (FIRST) radio stars. The emission mechanism is thermal bremsstrahlung (cm), and thermal dust (sub-mm, and even cm).

    Cool Main Sequence stars: the ultra-cool ones (beyond M7) are also a mystery, with radio emission greater than expected from the GĂźdel-Benz relation, only a minority being radio stars, and some very strong magnetic fields. ~constant broadband emission and periodic, pulse-like flares seem common (among those which are radio stars), and rotation and radio luminosity are correlated. Many cool MS stars, not just ultra-cool ones, produce flares, across the whole spectrum; these are similar to our Sun's (particularly the coronal mass ejections) in their astrophysics, but there are also important differences (e.g. the observed SEDs - spectral energy distributions - differ, leading to puzzling conclusions re magnetic field strengths).

    Stellar Winds: a.k.a. mass loss has been studied, radio astronomy-wise, by molecular line emission (cool stars) and free-free emission (hot stars), with the winds modeled as (sometimes clumpy) nested thermal sources. Except for the periodic, evolved stars (next), stars' winds are weak radio sources.

    Evolved stars: red giants and supergiants, regular and irregular variables, incipient planetary nebulae, lots to study! HI and CO line emission has been observed from many of these stars, including some resolved extended emission (and maybe giant starspots on some red giants). I found the most interesting radio emissions to be the masers: OH, H2O, SiO from oxygen-rich stars, and HCN, SiS, and CS from carbon-rich ones. The "envelope" around stars on their way to being white dwarfs (the envelope is called the circumstellar, CSE; the stars are post-AGB (asymptotic giant branch) and nascent planetary nebulae (PNe)) contains many chemical compounds ("species"), which can emit in the radio; over 80 such have been observed.

    White Dwarf binaries: In particular, cataclysmic variables (CVs) and symbiotic stars, which are binaries where the "other star" is losing mass to the white dwarf. The radio emission arises from thermal bremsstrahlung and synchrotron
    emission from particles accelerated in shocks (jets). The most spectacular CVs (other than supernovae) are novae; what's cool (!) about these radio stars is that the changes in radio emission by frequency and time can be modeled as an expanding sphere which becomes transparent (and so optically thin) in a well-ordered sequence.

    Pulsars: {they're radio stars, of a very special kind! not covered in Matthews 2014}

    There are a couple of sentences in the Conclusion that are well worth quoting, because they point to the need for more projects like RGZ, and for more citizen scientists to get involved in research beyond 'clicking to classify' (this is a particular hobby horse of mine):

    A concern voiced by several participants related to the growth of data volumes at rates that have already begun to challenge or exceed astronomers’ ability to handle them. [...] There was a consensus that given the rich, multi-dimensional nature of the data sets expected from current and planned radio facilities, essentially all data sets will effectively be “legacy” data with the potential to be mined for future science well beyond the goals or needs of the original proposal.

    The GĂźdel-Benz relation: A tight empirical correlation between the quiescent radio and x-ray luminosity of radio stars. First proposed in GĂźdel&Benz (1993), it has been shown to hold over ~ten orders of magnitude (independent of age, spectral class, whether in a binary or not, rotation, and photospheric/chromospheric activity), and it implies a strong relationship between the non-thermal electrons
    responsible for the radio emission and the thermal plasma giving rise to the x-rays (causation is not - yet - established).

    {other stuff: check out what Matthews references, and cites to it; dive into Helfand+ 1999 The FIRST Unbiased Survey for Radio Stars link 40 citations; Umana+ 2015 SCORPIO: A deep survey of Radio Emission from the stellar life-cycle astro-ph link}

    Catalogs of Radio Stars: {VizieR Catalogue of Radio Stars (Wendker, 2001) link, VizieR Radio emission from stars at 250GHz (Altenhoff+, 1994) link}

    Note: I intend to update this, and other posts by me in this thread (except the first), with details (and corrections) as I learn of/find them.

    Posted

  • JeanTate by JeanTate

    What's the latest news about radio stars?

    {placeholder}

    Note: I intend to update this, and other posts by me in this thread (except the first), with details (and corrections) as I learn of/find them.

    Posted

  • JeanTate by JeanTate

    Radio stars and FIRST

    RGZ is based on FIRST only, which observes at 1.4 GHz. So what do known radio stars look like in FIRST? Here in RGZ?

    {this is where my real work gets done: get lists of known radio stars and match them with ARG fields, using TOPCAT}

    What are the known ARG radio stars' SDSS mags and colors? their spectra? ditto WISE? In RGZ we have easy access to both SDSS and WISE, and obtaining {...}

    {placeholder}

    Note: I intend to update this, and other posts by me in this thread (except the first), with details (and corrections) as I learn of/find them.

    Posted

  • JeanTate by JeanTate

    What can we RGZ volunteers do?

    Here are my suggestions, for how we can actively contribute to research into radio stars.

    Help find radio star candidates:

    Once you've classified an ARG field:

    1. Click on Discuss
    2. That will open an Object Comment page on that field. If you can, identify host (or hosts) using SDSS
    • Click on the SDSS link
    • Then select what you think are the hosts
    • Then select Examine to bring up a new SDSS page
    1. If any of the hosts are classed as STAR (under Type, top right of the middle panel), note them
    2. If there's a spectrum (bottom part of the middle panel), and if it identifies the STAR as a STAR in the class field at the right, add the hashtag #specstar
    3. Then Create a New Post in the Science section {or do this only after 8?}
    4. If there's no spectrum, click on NED search in the left panel, to open a new page
    5. The first entry should be your target STAR. If it has a value in the z column, and that value is > 0.001, then what you found is not a Milky Way radio star
    6. Otherwise, it may be a radio star; add the hashtag #rscand (radio star candidate).

    {Other things? e.g. search for ARG fields in which a star may be a host}

    {more?}

    Note: I intend to update this, and other posts by me in this thread (except the first), with details (and corrections) as I learn of/find them.

    Posted

  • JeanTate by JeanTate

    Status

    A temporary post to record the current status of the preceding posts in this thread.

    The first three posts are ~done (minor edits only).

    The fourth is ~half done (depends on what I find once I start chasing refs/cites in earnest); the fifth is just a placeholder.

    The sixth? Lots of work still to do!

    Seventh: the main part is ~done, but other things we volunteers can do need to be thought up and added (what are your inputs, dear reader?)

    Posted

  • sisifolibre by sisifolibre

    Thanks Jean! great job, I'm learning a lot with this. Another motivation for explore RGZ!

    I'm taking a look on my collections searching for objects like this. The trouth is that I haven't seen any feedback about this objects by the staff, or the only feedback I remember has been something like "-hey it can't be a star, forget it-", sadly my suspect is that I have passed off some interesting subjects...

    Posted

  • sisifolibre by sisifolibre

    https://radiotalk.galaxyzoo.org/#/subjects/ARG000356z SDSS J230056.01+091403.8
    SDSS J230056.01+091403.8 -- Quasar On Simbad.
    . GAIA id 2714693727942891008

    enter image description here

    Posted

  • JeanTate by JeanTate in response to sisifolibre's comment.

    I think some on the Science Team are indeed interested in radio stars, or perhaps just a subset of them. However, I think all members already have their plates more than full (to use an English idiom) with cool and interesting things to follow. I don't know if it was always like this, but with the advent of big surveys - and, even more, the resources to combine them, like RGZ itself - there's always going to be more than even the whole world of professional astronomers can follow up on.

    Here's a broader context:

    Getting on for a year and half ago now, john_murrell started a discussion in Zooniverse Talk, Are there more serendipidous discoveries waiting to be followed up ?. This part of a post by zookeeper (Chris Lintott) is relevant:

    On the broader question - I think @JeanTate is right to highlight the gap between 'spotting something unusual' and getting enough people with enough skills to focus on what's been found to get it to the point where we can write a paper or apply for telescope time. At present, despite heroic efforts from a few Zooites, that gap is I think too large for most people to cross. It's something we'd like to work on.

    (It's a response to an earlier one of mine, extract:)

    The story of the discovery of the nature of AS Sco is, I think, a good illustration of why merely informing a professional that you've found "something odd" is inadequate, in an LSST era: there will be thousands of potential AS Sco's in that data, and thousands of "something odd"s. Unless many thousand new astronomy PhDs will magically appear, people willing to devote a significant amount of their time for no pay, the serendipitous discoveries won't happen (well, some will, but most won't). Citizen scientists need to be able to do good, independent investigations and research ... better to teach some CSs to fish than simply give them fish every day (so to speak).

    Well, here's one effort (heroic or not 😉) to follow up, led by us citizen scientists no less! 😄

    Posted

  • planetaryscience by planetaryscience in response to sisifolibre's comment.

    Unfortunately that one seems to actually be a weird-colored quasar.

    Posted

  • sisifolibre by sisifolibre

    If I remember well, I have read somewere that most of the "puntual" or compact in FIRST sources was discarded for RGZ. If this is correct, we can spect that most of the possible #radiostars compact emission from FIRST wouldn't be in RGZ?

    Posted

  • JeanTate by JeanTate in response to sisifolibre's comment.

    You are correct.

    In Banfield+ (2015) "Radio Galaxy Zoo: host galaxies and radio morphologies derived from visual inspection", Section 3.1.1 (sorry, I can't reproduce the equation, nor sub- and super-scripts):

    We designed Radio Galaxy Zoo to cross-match complex radio sources with their host galaxy rather than simple, compact radio sources which are easily matched by algorithms. We filtered the FIRST radio catalogue based on two criteria: (1) the radio source has a signal-to-noise ratio (SNR) greater than 10; and (2) the radio source is considered to be resolved. We considered a source to be resolved if it satisfies the criterion:

    {equation} (1)

    where Speak is the peak flux density in mJy beam^−1 and Sint is the total flux density of the radio source in mJy. This selection criterion is indicated by the blue solid line in Fig. 2 and selects 218,228 radio sources from the FIRST catalogue. At low peak fluxdensities the scatter around Speak/Sint = 1 rapidly increases due to intrinsic measurement errors on the peak and total fluxes, e.g. leading to unphysical situations where Speak > Sint. The larger number of sources below the Speak/Sint = 1 line corresponds to real extended sources. Assuming that the 34,689 radio sources found in the area that is mirroring the relation (the green dashed line) represents the 34,916 (16%) compact sources that can be expected in our sample and are useful for control purposes. At the time of publication, a random subset of 174,821 out of the 218,228 fields of 3′×3′ from the FIRST survey have been made available to Radio Galaxy Zoo participants.

    I'm not sure, but since then many of the remaining fields (perhaps all) have been added.

    Posted

  • sisifolibre by sisifolibre

    More simple questions...

    Why objects like SDSS J125326.70+060439.7 show spectrums like stars?

    It's due errors in the automatic clasification on SDSS?

    Or at last is not so sure that they are QSO?

    Posted

  • JeanTate by JeanTate in response to sisifolibre's comment.

    SDSS J125326.70+060439.7's spectrum very closely resembles that of a K0V star, except perhaps for the rather blue continuum. My inexperienced eye can see no sign of an overlap (foreground K0V star, background QSO) in the spectrum. What does Gaia DR2 have to say ... for example, does it have a non-zero parallax? proper motion? (within the uncertainties, of course)

    Posted

  • sisifolibre by sisifolibre

    Thanks Jean, seems that I had some wrong ideas. I read some coments ago like this one: https://radiotalk.galaxyzoo.org/#/subjects/ARG0002aur and other signed by @HAndernach about a known misclassification of a SDSS spectrum, and I was confusing some blazar spectrums with star spectrums.

    Now that I have take some time to read well and search subjects and comments I have a better idea... Anyway your comment help me with more to search about a possible #radiostar

    Posted

  • zutopian by zutopian

    • Paper:
    A Sample of Candidate Radio Stars in FIRST and SDSS
    http://arxiv.org/abs/0906.3030

    • Here is the list of the 112 radio star candidates.:
    http://iopscience.iop.org/0004-637X/701/1/535/fulltext/apj305758t1_mrt.txt

    • One of the candidates in RGZ Talk:
    https://radiotalk.galaxyzoo.org/#/boards/BRG0000002/discussions/DRG00006sg

    Posted

  • zutopian by zutopian

    Previously posted in the RGZ Journal Club:

    A Search for double-lobed radio emission from
    Galactic Stars and Spiral Galaxies    .
    Abiel Felipe Ortiz MartĂ­nez, Heinz Andernach

    We present a systematic search for two types of very unusual astronomical objects: Galactic stars and spiral galaxies with double radio lobes, i.e. radio emission on opposite sides of the optical object, suggesting the ejection of jets from them. We designed an algorithm to search for pairs of radio sources straddling objects from two unprecedented samples of 878,031 Galactic stars from the Sloan Digital Sky Survey and 675,874 spiral galaxy candidates drawn from the recent literature. We found three new examples of double-lobed radio stars, while for the spiral galaxies we only rediscovered one known such double source, confirming that the latter objects are extremely rare.

    (Submitted on 8 Oct 2016)
    https://arxiv.org/abs/1610.02572

    A Further Search for Galactic Stars with Double Radio Lobes

    Braulio Arredondo Padilla, Heinz Andernach

    Over a thousand stars in our Galaxy have been detected as radio emitters, but no normal stars are known to possess radio-emitting lobes similar to radio galaxies. Several recent attempts by us and other authors to find such objects remained inconclusive. Here we present a further search for double-lobed radio stars in two large samples of spectroscopic stars: over 20,000 white dwarves from the Sloan Digital Sky Survey (SDSS) DR12, and 2.5 million stars from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). These were cross-matched with sources from the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) survey at 1.4 GHz to look for source pairs straddling the stars with moderate symmetry about the stars. We found only four promising candidates for double-lobed radio stars, confirming they must be extremely rare. By comparison with SDSS, we inferred that about 16 per cent of LAMOST spectra may have erroneous classifications. We also rediscovered the giant radio galaxy J0927+3510 and propose a different, more distant host, suggesting a much larger radio size of 2.7 Mpc.

    (Submitted on 8 Dec 2017)
    https://arxiv.org/abs/1712.02920

    PS: H. Andernach is co-author!

    Posted

  • zutopian by zutopian

    Radio stars observed with LAMOST
    Authors: Zhang et al.

    The full text version of the paper is available for free.:

    Abstract:

    (...)We mined big data from the LAMOST spectral survey Data Release 2 (DR2), published on 2016 June 30, by cross-matching them with radio stars from FIRST and other surveys.(...)

    The criteria for selection were positional coincidence within 1.5‧‧ and LAMOST objects classified as stars.(...)

    https://www.researchgate.net/publication/320169338_Radio_stars_observed_in_the_LAMOST_spectral_survey?_sg=0cDRzZFcnU92_1VUu9S2ZCeJZNeMzq8TVfZ1dxWjTFeULcHCj5LDODzggNwvsAcmauXl419PeA

    Referring to my above post, which I did two days ago.:

    In the abstract of the 2nd paper there is given following statement.:

    A Further Search for Galactic Stars with Double Radio Lobes

    We found only four promising candidates for double-lobed radio stars, confirming they must be extremely rare. By comparison with SDSS, we inferred that about 16 per cent of LAMOST spectra may have erroneous classifications.

    @HAndernach

    • Did Zhang et al. miss some Radio stars because of erroneous classification?
    • Did they observe also those candidates of radio stars with lobes?

    Posted

  • zutopian by zutopian

    Referring to my posts on the 2nd page:

    Could the science team please inform about the Radio Zoo object IDs of the known radio stars,
    which were found by astronomers?

    • 4 candidates of double lobed radio stars.
    • List of 112 candidates FIRST/SDSS.
    • LAMOST radio stars

    Posted

  • zutopian by zutopian

    New paper:

    Radio pulsars: already fifty years!
    V.S.Beskin
    (Submitted on 23 Jul 2018).
    https://arxiv.org/abs/1807.08528

    Posted

  • zutopian by zutopian

    New paper:

    Radio Stars: from kHz to THz
    Lynn D. Matthews
    (Submitted on 25 Jul 2018)
    https://arxiv.org/abs/1807.09798

    Posted

  • zutopian by zutopian

    New paper:

    Parameters of the Link between the Optical and Radio Frames from Gaia DR2 Data and VLBI Measurements
    V. V. Bobylev
    (Submitted on 19 Dec 2018)

    Based on published data, we have assembled a sample of 88 radio stars for which there are both trigonometric parallax and proper motion measurements in the Gaia DR2 catalogue and VLBI measurements. (...)

    https://arxiv.org/abs/1812.07838

    Posted