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possible gravitational microlensing event in Taurus

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#1 robin_astro

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Posted 01 November 2017 - 08:22 AM

If you get the chance tonight it could be worthwhile looking at the star in Taurus at
05 07 42.64 +24 47 55.5 J2000
(DSS field attached)
and perhaps taking a low resolution spectrum. 
Normally mag 15, it is currently brightening rapidly, possibly reaching a maximum of mag 9.  It is likely to be a rare gravitational microlensing event where an unseen object passes between us and the star. If this is the case, the spectrum should remain unchanged as the brightness returns to normal.
Here is the current light curve
https://asas-sn.osu....74-ad0a8449925a

Interestingly I observed a similar event in Cassiopeia in 2006, being lucky to record the earliest spectrum confirming it was probably not a normal variable star using a Star Analyser
http://www.threehill.../spectra_30.htm

Cheers
Robin

Attached Thumbnails

  • pos_grav_microlens.png

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#2 NJScope

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Posted 01 November 2017 - 01:03 PM

Robin:

 

Thank you for bringing this very interesting event to our attention.  I might sneak a look at this target over the next few evenings using standard (BVIc) photometry.



#3 BrooksObs

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Posted 02 November 2017 - 02:00 PM

If you get the chance tonight it could be worthwhile looking at the star in Taurus at
05 07 42.64 +24 47 55.5 J2000
(DSS field attached)
and perhaps taking a low resolution spectrum. 
Normally mag 15, it is currently brightening rapidly, possibly reaching a maximum of mag 9.  It is likely to be a rare gravitational microlensing event where an unseen object passes between us and the star. If this is the case, the spectrum should remain unchanged as the brightness returns to normal.
Here is the current light curve
https://asas-sn.osu....74-ad0a8449925a

Interestingly I observed a similar event in Cassiopeia in 2006, being lucky to record the earliest spectrum confirming it was probably not a normal variable star using a Star Analyser
http://www.threehill.../spectra_30.htm

Cheers
Robin

 

I, too, witnessed that extraordinary event, discovered by an old acquaintance of mine A. Tago of Japan. The event took place around the very end of October 2006 with the transient (GSC 3656-1328) brightened by ~4.5 mag during a ~15 day period. It peaked at just below naked eye visibility on the night of maximum! As I recall, the event ran its course with little interference from moonlight and the star situated high up in the evening sky at the time. The situation couldn't have been better for observation!

 

BrooksObs


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#4 robin_astro

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Posted 02 November 2017 - 05:09 PM

It looks like this one has  peaked at Vmag 11.5 and it is now on its way down

http://www.astronome...org/?read=10923

http://www.astronomy...264_2447555.pdf

 

Here is my low resolution R ~500 spectrum from last night (blue). The features match those of a F5v reference star (red) but with significant interstellar redenning (green - target/F5v), in agreement with the high resolution spectrum reported here.

http://www.astronome...org/?read=10919

 

Robin

 

_tcpj05074264+2447555_20171101_971_leadbeater.png


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#5 RobboK

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Posted 03 November 2017 - 06:52 AM

The ASAS-SN light curve for TCP J05074264+2447555 shows it fading now (attached).  Also attached is my image from 01 Nov 2017, where it was about mag 11.5 (green channel, ~V).

 

Cheers -

 

Rob

 

TCP J05074264+2447555 light curve 23 Nov ASAS-SN 60 days.jpg

 

TCP J05074264+2447555, 01 Nov 2017 text.jpg



#6 gavinm

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Posted 04 November 2017 - 01:15 AM

Awesome to see amateurs (no offence intended if you consider yourself more than 'amateur') detecting and doing followup on these events.

When I was researching and had the pleasure of working with some of the MOA people there were a lot of these. In fact a few every night. The MOA telescope has a bank of computers analysing millions of stars in their FOV simultaneously. If an abnormal event was detected (key word abnormal), alerts were sent out for us to follow up.

In fact, the University of Ohio (from the link above) was one of the main followup groups. They are still after keen amateurs to work with them. Google microfun. We were searching for exoplanets. Sadly I no longer have access to the telescope I used so I'm out :(



#7 robin_astro

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Posted 04 November 2017 - 03:34 PM

Hi Gavin,

 

Yes I've seen some of the impressive light curves from microfun showing exoplanet lensing. I understand the  galactic bulge (sadly not accessible  from my northern latitude) where the pro surveys tend to look is a good hunting ground because of the high density of stars, increasing the probability of two in line of sight.  According to one of the pro astronomers I have been talking to involved in following these up, bright events away from the high density regions in the galactic plane like this are few and far between. ("a once in a decade event")  so that's this one and the one back in 2006, which I remember was treated with some initial scepticism because it was so unlikely and unexpected 

 

Cheers

Robin

 

EDIT: like the 2006 event this one was also initially discovered by an amateur in Japan

"Discovered by T. Kojima, Gunma-ken, Japan, who found this on three frames taken using Canon EOS 6D + 135-mm f3.2 lens with the limiting mag.= 13.0."

(from the  IAU CBAT transients follow up page)


Edited by robin_astro, 04 November 2017 - 03:47 PM.


#8 David Gray

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Posted 04 November 2017 - 06:12 PM

Observed this visually on these dates (UT):

 

Nov 2d. 00:50 Mag-est: 11.6; Seeing 7/10, Transparency Very Good; 94% Moon @ 65º W. 

 

Nov 2d. 23:25 Mag-est: 11.8; Seeing 6-7/10, Transparency Very Good; 98% Moon @ 54º W. 

 

Nov 4d. 22:40 Mag-est: 12.3/12.4 (Using AAVSO Chart); Seeing 5-6/10, Transparency Good but some thin cloud streaks; 99% Moon @ 26º W

 

415mm (16.3”) Dall-Kirkham 285x.

 

The first estimate (00:50) was in a very good sky but stars only roughly down to about a glimpsed mag. 14.5  due to moonlight.  That night the moon being out of sight beyond the rooftop.  The second estimate was through a cloud gap and the moon was handily hidden by cloud at the time of that estimate. 

 

Both nights the star – I understand to be F5 – had a lightish orange hue: similar to a mid/late K-star. 

 

The first two estimates were made by comparison with TYC 1849-1592-1:  mag. 11.37; as given in Sky Map Pro 12.

 

Tonight’s view was somewhat hampered with the moon; but with a black cloth over my head I could pick out the 13.6 star directly pretty well. But the  star close s’east of the lensed star was not seen by any means.

 

Hoping to post some impressions on the Sketching Forum in due course.

 

Dave.


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#9 NJScope

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Posted 05 November 2017 - 12:12 PM

I imaged this target (aka GSC 1849-1566) for 5.5 hours on Nov 3rd starting around 06:26 UTC and was able to observe a small but significant decrease in brightness in three different bandpasses (B, V and Ic).   The average value using APASS magnitude assignments for 5 comparison stars was V-mag = 11.79 ± 0.004 around 09:11 UTC while the change from the start of the run until the end was 0.057 V-mag.GSC 1849-1566_60sec_FOV_AIJ_v1.png GSC 1849-1566_BVIc-mag vs HJD_v1.jpg


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#10 robin_astro

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Posted 05 November 2017 - 07:34 PM

Hi Dave,

 

 

Both nights the star – I understand to be F5 – had a lightish orange hue: similar to a mid/late K-star. 

 

 

Your estimate of  the colour is pretty much spot on. Although actually an F5 star, as confirmed by the  lines in the spectrum, the shape of the continuum looks more like that of a K star  due to the reddening from interstellar extinction. 

 

Cheers

Robin


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#11 jaylyle

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Posted 05 November 2017 - 07:51 PM

This is so freakin' cool!



#12 NJScope

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Posted 05 November 2017 - 09:11 PM

The B-V color index estimated (0.862 ± 0.007) from my multi-color is consistent with a K8 star, however when corrected for reddening (E(B-V) = 0.4984 ±0.0167, the final value (0.366 ± 0.018) is consistent with an early F star.   Reddening values from the Schlafly & Finkbeiner (2011 ApJ 737, 103) derived interstellar dust maps tend to be overestimated for targets that are probably less than a 1 Kpc away, so an F5 classification is totally consistent. 

.


Edited by NJScope, 05 November 2017 - 09:12 PM.

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#13 gavinm

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Posted 05 November 2017 - 10:49 PM

Hi Robin, you're dead right - for someone to pick this up is an amazing effort. More so that there are amateurs getting really good data on it. I've never seen a spectrum on one of these before.

Congratulations :)



#14 David Gray

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Posted 06 November 2017 - 05:36 AM

Hi Dave,

 

 

Both nights the star – I understand to be F5 – had a lightish orange hue: similar to a mid/late K-star. 

 

 

Your estimate of  the colour is pretty much spot on. Although actually an F5 star, as confirmed by the  lines in the spectrum, the shape of the continuum looks more like that of a K star  due to the reddening from interstellar extinction. 

 

Cheers

Robin

Thanks Robin,

 

Good to know the colour-impression confirmed!

 

Last night it was tougher with the moon in the Hyades, and with it being Guy Fawkes/bonfire night transparency was all over the place!

 

But snatched a look at 22:20 UT in fairly good transparency and seeing 4-5/10: estimated 12.5 by comparison with the 12.8 star close south of that distinctive triangle in the east-field......16.3" D-K x285 (24mm ES Maxvision 18' FOV).

 

Dave.


Edited by David Gray, 06 November 2017 - 05:38 AM.


#15 Aquarellia

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Posted 06 November 2017 - 05:57 AM

Another interesting object after the CTA102 one!

Tonight 05/06 nov. desepite the moonlight I was able to post a visual estimation based on the AAVSO chart. : +12.4 between the +12.0 and +12.6 references stars.

Some other info on the sketching forum: https://www.cloudyni...observe-it-now/

Michel



#16 NJScope

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Posted 15 November 2017 - 06:36 PM

I have continued following this system photometrically.  Last night's data indicate that it is now at V-mag = 13.318 ±0.006.  Interestingly, about a week ago the Astronomer's Telegram issued a tantalizing report that this microlensing event may have uncovered a very low mass ratio component that might suggest a new planetary system.  The lightcurve and model fit can be seen here.


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#17 Phil Shaffer

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Posted 17 November 2017 - 12:17 PM

Awesome to see amateurs (no offence intended if you consider yourself more than 'amateur') detecting and doing followup on these events.

When I was researching and had the pleasure of working with some of the MOA people there were a lot of these. In fact a few every night. The MOA telescope has a bank of computers analysing millions of stars in their FOV simultaneously. If an abnormal event was detected (key word abnormal), alerts were sent out for us to follow up.

In fact, the University of Ohio (from the link above) was one of the main followup groups. They are still after keen amateurs to work with them. Google microfun. We were searching for exoplanets. Sadly I no longer have access to the telescope I used so I'm out frown.gif

The University of Ohio !! (ARGGHHHH)  (feigning horror). It's actually The Ohio State University here in Columbus - excellent astronomy department. Dr. Kris Stanek gave the Columbus Astronomical Soceity a talk on the ASASSN project on 11/9. Really interesting. Amazing ability to crank data. They have to exclude about 50,000 known asteroids on each nights data. But it still comes down to having to review "by hand" a large number of candidate transients every day. And yes they do like input from some amateurs. Even those using iTelescope can be useful to the project. 


Edited by Phil Shaffer, 17 November 2017 - 12:53 PM.


#18 NJScope

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Posted 18 November 2017 - 04:49 PM

Phil:

 

Gavin is a Kiwi, so he can be forgiven for mixing up Univ of Ohio with Ohio State Univ.  BTW, Robin put me in direct contact with Dr. Subo Dong at OSU so I regularly update him with V-mag data from this system.


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#19 Phil Shaffer

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Posted 19 November 2017 - 07:00 AM

Oh, I wasn't truly offended, but as an Ohio State grad, well, you just have to say something. 

One interesting thing the OSU astronomy department does is have "morning coffee" which is essentially an informal research seminar for the faculty and grad students, but it is open to the public. I have been only once, but it was fascinating on several levels. Also - there were probably 20 or so non faculty members (i.e. just regular people like me) there to listen. 

I have a friend, Isaac Cruz, who has his own remote observatory in New Mexico. Stanek has asked him at least once to verify a new SN candidate, so the faculty at OSU maintain their contacts with the amateur community to help them out when they can.




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