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Stellar News Feed Archive

How Many Stars Are In The Universe? Tuesday, June 3, 2014 - 10:09

Looking up into the night sky, it's challenging enough for an amateur astronomer to count the number of naked-eye stars that are visible. With bigger telescopes, more stars become visible, making counting impossible because of the amount of time it would take. So how do astronomers figure out how many stars are in the universe?

The first sticky part is trying to define what "universe" means. Even if we narrow down the definition to the "observable" universe — what we can see — estimating the number of stars within it requires knowing just how big the universe is. The first complication is that the universe itself is expanding, and the second complication is that space-time is curved.

Read the rest of the story at Space.com
 

Does the Period of a Pulsating Star Depend on its Amplitude? Friday, May 30, 2014 - 10:00

Several classes of pulsating stars are now known to undergo slow changes in amplitude; these include pulsating red giants and supergiants, and yellow supergiants. We have used visual observations from the AAVSO International Database, and wavelet analysis of 39 red giants, 7 red supergiants, and 3 yellow supergiants, to test the hypothesis that an increase in amplitude would result in an increase in period, because of non-linear effects in the pulsation. For most of the stars, the results are complex and/or indeterminate, due to the limitations of the data, the small amplitude or amplitude variation, or other processes such as random cycle-to-cycle period fluctuations. For the dozen stars which have substantial amplitude variation, and reasonably simple behavior, there is a 75-80% tendency to show a positive correlation between amplitude and period.

Authors: John R. Percy, Jeong Yeon (JY) Yook

Read the paper on astro-ph
 

AAVSO Acronym of the Day: VPhot Friday, May 30, 2014 - 09:45

Today's acronym of the day is VPhot – Variable Star Photometry Software

                      

VPhot is an online tool for photometric analysis. You can upload your own FITS images to VPhot or have images taken via AAVSOnet automatically sent to your VPhot account. All VPhot processing is done via a web browser. All of the basic photometry tools exist (stacking, time series analysis, control of annulus', transformation, etc.) and the algorithms have been rigorously checked and confirmed to be of the highest quality. Results of the processing are automatically exported in AAVSO Extended Format, meaning you can directly load them into our database via WebObs without having to make any changes to the data file. VPhot is only available to AAVSO members.

This is just one example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

A new method for cosmic distances: using active galactic nuclei Thursday, May 29, 2014 - 13:07

Adam Riess, co-discoverer of the accelerating expansion of the Universe due to dark energy, visited Harvard last year, where he told me a story about his time in grad school there.  He recalled hearing a lecture on the uncertainty in the rate at which the Universe is expanding and thinking, “That problem will never be solved.”  Twenty years on, we know the local expansion rate (called the Hubble constant, or H0) to about 4% precision, and many different, independent techniques find mutually consistent values. However, measuring the Hubble constant remains one of the most important problems in cosmology because it is intimately connected to the Universe’s contents.  In particular, General Relativity means that the Universe’s contents set its expansion rate, and so precise measurement of the expansion rate can probe the amount and evolution of different components of the Universe.

Thus, it is exciting when a new, independent method of measuring the expansion rate (H0) is proposed—and even more exciting when it works. In the short paper I discuss today, the authors show that time delays in the light emitted from distant, violently variable galactic centers (“active galactic nuclei”, or AGN) can probe H0 with precision similar to that of the Hubble Space Telescope—and out to about twice the distance.

Read the rest on Astrobites
 

AAVSO Acronym of the Day: LCG Thursday, May 29, 2014 - 10:18

The AAVSO Acronym of the Day today is LCG – The AAVSO Light Curve Generator

Observations of variable stars are plotted on a graph called a light curve as the apparent brightness (magnitude) versus time, usually in Julian Date (JD). The light curve is the single most important graph in variable star astronomy. Light curves allow astronomers to unlock some of the secrets of variable stars. The AAVSO Light Curve Generator allows anyone to plot light curves using data on thousands of stars stored in the AAVSO International Database. It is one of the most popular tools on the AAVSO website. 

This is another example of the tools the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.

 

The M4.5V flare star AF Psc as seen in K2 engineering data Thursday, May 29, 2014 - 10:09

We present the light curve of the little studied flare star AF Psc (M4.5V) obtained using engineering data from the K2 mission. Data were obtained in Long Cadence mode giving an effective exposure of 29 min and nearly 9 d of coverage. A clear modulation on a period of 1.08 d was seen which is the signature of the stellar rotation period. We identify 14 flares in the light curve, with the most luminous flares apparently coming from the same active region. We compare the flare characteristics of AF Psc to two M4V flare stars studied using kepler data. The K2 mission, if given approval, will present a unique opportunity to study the rotation and flare properties of late type dwarf stars with different ages and mass.

Authors: Gavin Ramsay, J. Gerry Doyle (Armagh Observatory) 

Read the paper on astro-ph
 

Revised age for CM Draconis and WD 1633+572: Toward a resolution of model-observation radius discrepancies Thursday, May 29, 2014 - 09:55

We report an age revision for the low-mass detached eclipsing binary CM Draconis and its common proper motion companion, WD 1633+572. An age of 10±2 Gyr is found by combining an age estimate for the lifetime of WD 1633+572 and an estimate from galactic space motions. The revised age is greater than a factor of two older than previous estimates. Our results provide consistency between the white dwarf age and the system's galactic kinematics, which reveal the system is a highly probable member of the galactic thick disk. We find the probability that CM Draconis and WD 1633+572 are members of the thick disk is 8500 times greater than the probability that they are members of the thin disk and 170 times greater than the probability they are halo interlopers. If CM Draconis is a member of the thick disk, it is likely enriched in α-elements compared to iron by at least 0.2 dex relative to the Sun. This leads to the possibility that previous studies under-estimate the [Fe/H] value, suggesting the system has a near-solar [Fe/H]. Implications for the long-standing discrepancies between the radii of CM Draconis and predictions from stellar evolution theory are discussed. We conclude that CM Draconis is only inflated by about 2% compared to stellar evolution predictions.

Authors: Gregory A. Feiden and Brian Chaboyer

Read the paper on astro-ph
 

AAVSO Acronym of the Day: SeqPlot Wednesday, May 28, 2014 - 08:08

Today's acronym of the day features one of the AAVSO's tools, SeqPlot – The AAVSO Sequence Plotter.

SeqPlot is a platform independent Java Web Start application. It accesses an on-line MySQL database that contains more than 47 million stars that have been calibrated through the AAVSO Photometric All-Sky Survey (APASS), USNO-Flagstaff, Sonoita, and other AAVSOnet telescopes. The General Catalogue of Photometric Data (GCPD) and Tycho-2 catalogs are also included. You can plot fields using either a field name or by coordinates and field size. Users can select stars for a sequence and write them to a text file in the correct format for uploading to VSD.

This is just one example of the tools the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

'Wolf-Rayet' Supernova Observed --"Its Flash Ionized Its Immediate Surroundings Followed by Powerful Blast Wave" Tuesday, May 27, 2014 - 22:07

Wolf-Rayet stars are very large and very hot. Astronomers have long wondered whether Wolf-Rayet stars are the progenitors of certain types of supernovae. New work from the Palomar Transient Factory team is homing in on the answer. They have identified a Wolf-Rayet star as the likely progenitor of a recently exploded supernova. When the supernova exploded, its flash ionized its immediate surroundings, giving the astronomers a direct glimpse of the progenitor star's chemistry. This opportunity lasts only for a day before the supernova blast wave sweeps the ionization away. So it's crucial to rapidly respond to a young supernova discovery to get the flash spectrum in the nick of time.

Read the rest of the story at The Daily Galaxy
 

AAVSO Acronym of the Day - eJAAVSO Tuesday, May 27, 2014 - 08:19

Today's AAVSO Acronym is eJAAVSO – The Electronic Journal of the AAVSO             

                       

eJAAVSO is the online counterpart of The Journal of the American Association of Variable Star Observers. The eJAAVSO consists of papers that have been refereed, edited, and accepted for publication in the paper edition of the Journal. Its purpose is to speed and broaden the dissemination of variable star research to the global astronomical community, and make papers available to interested parties. All papers and abstracts from 1972 to the present are accessible to all readers via the eJAAVSO page. In addition, a PDF file of each complete issue of The Journal from Volume 36 on is available free of charge to members via the eJAAVSO page. 

This is just one example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

AAVSO Acronym of the Day: VPhot Friday, May 23, 2014 - 08:16

Today's acronym is VPhot – Variable Star Photometry Software

                               

VPhot is an online tool for photometric analysis. You can upload your own FITS images to VPhot or have images taken via AAVSOnet automatically sent to your VPhot account. All VPhot processing is done via a web browser. All of the basic photometry tools exist (stacking, time series analysis, control of annulus', transformation, etc.) and the algorithms have been rigorously checked and confirmed to be of the highest quality. Results of the processing are automatically exported in AAVSO Extended Format, meaning you can directly load them into our database via WebObs without having to make any changes to the data file. VPhot is only available to AAVSO members.

The Catalina Surveys Periodic Variable Star Catalog Friday, May 23, 2014 - 08:07

We present ~47,000 periodic variables found during the analysis of 5.4 million variable star candidates within a 20,000 square degree region covered by the Catalina Surveys Data Release-1 (CSDR1). Combining these variables with type-ab RR Lyrae from our previous work, we produce an on-line catalog containing periods, amplitudes, and classifications for ~61,000 periodic variables. By cross-matching these variables with those from prior surveys, we find that > 90% of the ~8,000 known periodic variables in the survey region are recovered. For these sources we find excellent agreement between our catalog and prior values of luminosity, period and amplitude, as well as classification. We investigate the rate of confusion between objects classified as contact binaries and type-c RR Lyrae (RRc's) based on periods, colours, amplitudes, metalicities, radial velocities and surface gravities. We find that no more than few percent of these variables in these classes are misidentified. By deriving distances for this clean sample of ~5,500 RRc's, we trace the path of the Sagittarius tidal streams within the Galactic halo. Selecting 146 outer-halo RRc's with SDSS radial velocities, we confirm the presence of a coherent halo structure that is inconsistent with current N-body simulations of the Sagittarius tidal stream. We also find numerous long-period variables that are very likely associated within the Sagittarius tidal streams system. Based on the examination of 31,000 contact binary light curves we find evidence for two subgroups exhibiting irregular lightcurves. One subgroup presents significant variations in mean brightness that are likely due to chromospheric activity. The other subgroup shows stable modulations over more than a thousand days and thereby provides evidence that the O'Connell effect is not due to stellar spots.


Authors: A.J. Drake, M.J. Graham, S.G. Djorgovski, M. Catelan, A.A. Mahabal, G. Torrealba, D. Garcia-Alvarez, C. Donalek, J.L. Prieto, R. Williams, S. Larson, E. Christensen, V. Belokurov, S.E. Koposov, E. Beshore, A. Boattini, A. Gibbs, R. Hill, R. Kowalski, J. Johnson, F. Shelly

Read the paper on arXiv

AAVSO Acronym for the Day: MNF Wednesday, May 21, 2014 - 13:30

Today we feature another electronic publication of the AAVSO, MNF – MyNewsFlash

MyNewsFlash allows you to set up a method of automatically emailing or texting you the current activity of your favorite star, or class of stars. This is a VERY customizable service. MyNewsFlash can send you the most recent AAVSO variable star observations on whatever stars you choose, at whatever magnitude cutoff you choose, delivered in the format of your choice, at a frequency that you choose.

This is just another example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.

 

Revealing the Complex Outflow Structure of Binary UY Aurigae Wednesday, May 21, 2014 - 08:27

Because many stars form together as companions in binary or multiple systems, investigating these systems is essential for understanding star and planet formation. Although jets (i.e., narrow bright streams of gas) and outflows (i.e., less collimated flows of gas) from single young stars are ubiquitous, only a few observations have shown jets or outflows from multiple, low-mass young stars. Therefore, the current team chose to examine the outflow structure of binary UY Aur, which is a close binary system composed of young stars separated by less than an arcsecond (0".89).

UY Aur has a very complicated structure. Both the primary star (UY Aur A, more massive and brighter) and the secondary star (UY Aur B, fainter and cooler) have small circumstellar disks (disks of gas and material orbiting around them). In addition, a circumbinary disk surrounds the two stars. Such disks are difficult to detect, and this is only the second disk of this type that has been resolved and imaged. Receding ("redshifted") jets have been observed, and approaching ("blueshifted") ones have been reported for this system. However, their driving sources are not clear, because the spatial resolution of the images was too low (> one arcsecond).

Read the full press release from the Subaru Telescope site

 

AAVSO Acronym of the Day: JAAVSO Tuesday, May 20, 2014 - 15:41

Today's acronym is JAAVSO – The Journal of the AAVSO

The Journal of the American Association of Variable Star Observers (ISSN 0271-9053) is the research publication of the AAVSO. The Journal contains scholarly research articles submitted by members of the AAVSO community on a wide range of topics relevant to the AAVSO and variable star astronomy. The Journal is a refereed publication, open to any and all amateur and professional members of the variable star research and observation community, as well as related scholarly groups such as computer and information scientists, historians, and educators. The Journal is also the primary publication for papers and abstracts presented at AAVSO meetings.  

 This is just one example of the publications and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

Fundamental parameters of RR Lyrae stars from multicolour photometry and Kurucz atmospheric models -- III. SW And, DH Peg, CU Com, DY Peg Monday, May 19, 2014 - 14:44

We report the most comprehensive UBV(RI)_C observations of the bright, radially pulsating field stars SW And, DH Peg, CU Com, DY Peg. Long term variation has been found in the ultraviolet colour curves of SW And and DH Peg. We apply our photometric-hydrodynamic method to determine the fundamental parameters of these stars: metallicity, reddening, distance, mass, radius, equilibrium luminosity and effective temperature. Our method works well for SW And, CU Com and DY Peg. A very small mass 0.26+/-0.04 M_Sun of SW And has been found. The fundamental parameters of CU Com are those of a normal double-mode RR Lyrae (RRd) star. DY Peg has been found to have paradoxical astrophysical parameters: the metallicity, mass and period are characteristic for a high-amplitude Delta Sct star while the luminosity and radius place it in the group of RR Lyrae stars. DH Peg has been found to be peculiar: the definite instability in the colour curves towards ultraviolet, the dynamical variability of the atmosphere during the shocked phases suggests that the main assumptions of our photometric-hydrodynamic method, the quasi-static atmosphere approximation (QSAA) and the exclusive excitation of radial modes are probably not satisfied in this star. The fundamental parameters of all stars studied in this series of papers are summarized in tabular and graphical form.

Authors:  S. Barcza, J. M. Benkő

Read the full paper at astro-ph

AAVSO Acronym of the Day: CHOICE Monday, May 19, 2014 - 13:40

Today's featured acronym is CHOICE – The Carolyn Hurless Online Institute for Continuing Education

CHOICE is an education and outreach initiative of the AAVSO. It is a collection of informal, online short courses on topics chosen to help members of the AAVSO and others contribute more to science. Most CHOICE courses are four weeks long. They are run via the AAVSO web site using private forums and e-mail at a self-directed pace. One of the unique aspects of this program is that courses are peer taught. That is, graduates of one course have the opportunity to teach the next iteration of that course. Those who successfully complete a course are provided with a certificate and a badge displayed on their web site user profile page. We hope to increase the impact of this program by offering many of the courses to non-members.

This is just one example of the programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

Long-term optical and radio variability of BL Lacertae Saturday, May 17, 2014 - 17:28

Well-sampled optical and radio light curves of BL Lacertae in B, V, R, I bands and 4.8, 8.0, 14.5 GHz from 1968 to 2014 were presented in this paper. A possible $1.26 \pm 0.05$ yr period in optical bands and a $7.50 \pm 0.15$ yr period in radio bands were detected based on discrete correlation function, structure function as well as Jurkevich method. Correlations among different bands were also analyzed and no reliable time delay was found between optical bands. Very weak correlations were detected between V band and radio bands. However, in radio bands the variation at low frequency lagged that at high frequency obviously. The spectrum of BL Lacertae turned mildly bluer when the object turned brighter, and stronger bluer-when-brighter trends were found for short flares. A scenario including a precessing helical jet and periodic shocks was put forward to interpret the variation characteristics of BL Lacertae.

Authors:  Y. C. Guo, S. M. Hu, C. Xu, C. Y. Liu, X. Chen, D. F. Guo, F. Y. Meng, M. T. Xu, J. Q. Xu

Read the paper on astro-ph

Pulsing Stars Help Map Milky Way's Outer Reaches Saturday, May 17, 2014 - 13:06

New observations of five young variable stars reveal a strange thickening in farflung regions of the Milky Way galaxy.

Known as Cepheid variables, the stars are positioned above and below the plane of the galaxy's disk. That position, combined with the stars' young age, indicates a warp to the arm that was previously suggested by observations of dust, but had not been shown by the presence of stars.

Stars on the other side of the galactic center can be challenging for scientists to observe, as the amount of interstellar dust increases at greater distances. A team of astronomers utilized two telescopes at the South African Astronomical Observatory (SAAO) to determine that the five Cepheid variables lie on the far side of the bulge of material in the heart of the Milky Way, above and below the galactic plane.

Read the full story on Space.com

AAVSO Acronym of the Day: VSOTS Saturday, May 17, 2014 - 12:31

Today's acronym is VSOTS – Variable Star of the Season


The “Variable Star of the Season” series of articles originated in 1998 as the "Variable Star of the Month". The articles contain useful and interesting information on individual variable stars. Many of the most popular stars in the AAVSO observing program are featured. From 2002 to 2011, they have all been published as part of the "Variable Star of the Season" collection. Each article is now archived in the VSOTS Archive and available in either .html or .pdf format.

This is another example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.

 

AAVSO Acronym of the Day: CHET Friday, May 16, 2014 - 17:53

CHET – Chart Error Tracking Tool

CHET was created to track of all reported issues with AAVSO variable star charts and sequences and the chart and sequence team’s progress in addressing those issues. Information reported to CHET by observers is used to evaluate and prioritize the work done by the charts and sequences team. When the team makes revisions or corrections, CHET automatically sends an email notification to the observer who reported the issue. The improvement in the quality of charts and sequences, and the speed with which new sequences are created for new transient objects, in the last ten years, is nothing short of amazing.

 This is just one example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

AAVSO Acronym of the Day: WebObs Wednesday, May 14, 2014 - 09:08

Today's acronym is WebObs – Web-based Observation Submission Tool

WebObs is the tool 99% of our observers use to submit observations to the AID. You can submit observations one at a time using the individual observation form, or you can upload files containing hundreds or thousands of observations all at once using the file upload feature. Files must conform to the AAVSO File Form Specifications which are described in detail on the website.

You can also use WebObs to search for observations of any variable star, or search for your own observations, which you can view, edit or delete. It can be used to download your observations for a specific time frame or all the observations you have ever reported to the AID. Registered photoelectric photometrists may also upload unreduced data to WebObs.

This is just one example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.
 

Magnetar Formation Mystery Solved? Wednesday, May 14, 2014 - 08:57

Magnetars are the bizarre super-dense remnants of supernova explosions. They are the strongest magnets known in the Universe — millions of times more powerful than the strongest magnets on Earth. A team of European astronomers using ESO’s Very Large Telescope (VLT) now believe they’ve found the partner star of a magnetar for the first time. This discovery helps to explain how magnetars form — a conundrum dating back 35 years — and why this particular star didn’t collapse into a black hole as astronomers would expect.

It seems that being a component of a double star may therefore be an essential ingredient in the recipe for forming a magnetar. The rapid rotation created by mass transfer between the two stars appears necessary to generate the ultra-strong magnetic field and then a second mass transfer phase allows the magnetar-to-be to slim down sufficiently so that it does not collapse into a black hole at the moment of its death.

Read the full story on ESO Science Release 1415

Hidden nurseries in the Milky Way Tuesday, May 13, 2014 - 16:14

The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) survey has revealed an unprecedented number of cold dense clumps of gas and dust as the cradles of massive stars, thus providing a complete view of their birthplaces in the Milky Way. Based on this census, an international team of scientists led by Timea Csengeri from the Max Planck Institute for Radio Astronomy in Bonn has estimated the time scale for these nurseries to grow stars. This has been found to be a very fast process: with only 75,000 years on average it is much shorter than the corresponding time scales typically found for nurseries of lower mass stars.

Read the press release from Max Plank Institute for Radio Astronomy

Get the pre-print of the research paper-  “The ATLASGAL survey: a catalog of dust condensations in the galactic plane,” T. Csengeri, J. S. Urquhart, F. Schuller, F. Motte, S. Bontemps, F. Wyrowski, K. M. Menten, L. Bronfman, H. Beuther, Th. Henning, L. Testi, A. Zavagno, M. Walmsley, Astronomy & Astrophysics, Vol. 565, A75 (May 2014).
 

AAVSO Acronym for the Day: AAVSOnet Tuesday, May 13, 2014 - 09:11

Today's AAVSO Acronym of the Day is AAVSOnet – The AAVSO robotic telescope network

AAVSOnet is a network of remote, robotically controlled, and automatically queued telescopes for the use of AAVSO members. Several telescopes, located worldwide, are currently active and taking data right now. The entire network is founded on the generosity and dedication of AAVSO volunteers, donors and corporate sponsors. 

Even the telescopes in the network have acronyms to describe them!

BSM – Bright Star Monitor, several small (~60mm) telescopes located in Australia and the USA.
C30 – Coker 30cm telescope, located in Sutter Creek, California, donated to the AAVSO by Phillip Coker.
OC61 – Optical Craftsman 61cm telescope, located at the Mount John University Observatory in New Zealand.
SRO – Sonoita Research Observatory, a 50cm telescope located in a private facility in Sonoita, Arizona.
TMO61 – Tortugas Mountain 61cm telescope, part of the new Mexico State University Observatory, located on Tortugas mountain in New Mexico.

This is another example of the tools and programs the AAVSO provides to its members, observers and the astronomical community. Please help support these services by contributing to this year's Annual Campaign.

You can mail a check to AAVSO headquarters, or you can make a donation online. Just click the Donate Now button on our home page and select Annual Campaign in the drop down menu.

THANK YOU FOR YOUR SUPPORT!

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