Potential white dwarf near M27

While carefully examining the FITS from an already published image of M27, next to this planetary nebula I noticed an anomalously blue star-like object that interested me extremely, since nothing similar is observed nearby. Trying to figure out what it was, a whole investigation began, a detective story, since I could not find anything about it anywhere, except that I came across one of the so-called **"super blue stars"** in the field of M27. This is a known and very interesting phenomenon that astrophotographers often notice in deep images of this nebula, and it has a quite specific astrophysical explanation. It appears that this is most likely a white dwarf (or a white dwarf candidate). It was said that according to Gaia DR3 data, several stars in the immediate vicinity of the edge of M27 are classified as **white dwarf candidates**. This is not part of the nebula, but independent stars located either in the foreground (much closer to us) or in the background, which simply happen to be projected onto the edge of the nebula from our point of view. Why are they so intensely blue? **Because of temperature.** Like the central star of M27, white dwarfs have a very high surface temperature. Their spectral peak is shifted into the ultraviolet and blue region. Bright blue stars in images usually look white with a bluish halo, because during processing all three channels (R, G, B) are overexposed (saturated) and blend into white. But these "super blue" stars are fairly faint (usually around 15–17m). When you stretch the histogram to reveal the faint nebula, the signal in the blue channel of such a hot star becomes dominant, while the red and green channels remain almost empty. As a result, the star acquires that very unnatural, saturated, "acid" blue color that stands out sharply against the background of the others.

I decided to recheck this version more thoroughly. I selected a 3×3 pixel area directly on the star. Here are the raw data:

- **Red (R):** mean = 15,408
- **Green (G):** mean = 19,075
- **Blue (B):** mean = **21,562**

It is clear that the blue channel really stands out anomalously! Here one more point should be taken into account — the **CFA pattern.** The ASI533MC camera uses a Bayer matrix (RGGB). In it, there are twice as many green pixels as red or blue. Therefore, the "raw" signal in the green channel is always inflated simply because of the number of sensors. To get a fair comparison of colors, the green channel value needs to be divided by 2.

**The normalized values are as follows:**

- **Red:** 15,408
- **Green:** 19,075 / 2 ≈ **9,537**
- **Blue:** **21,562**

**Conclusion from the image:** The ratio of signals: **Blue (21.5k) > Red (15.4k) > Green (9.5k)**. This is the spectral signature of an extremely hot object. The peak of radiation falls in the blue/ultraviolet part of the spectrum, while in the red and green regions the signal drops sharply. Ordinary stars do not shine like this.

I ran the image through the part on **astronomical identification (Gaia DR3).** The cursor coordinates in the screenshot: **19h 59m 55s, +22° 41' 55"**. I queried the Gaia DR3 catalog for this point and found an object only 5 arcseconds from your cursor. That's definitely it!

**Data for the object Gaia DR3 1827244873458649600:**

- **Magnitude (Gmag):** 19.05m (the object is faint, so it is not in older catalogs such as SIMBAD/Hipparcos).
- **Parallax:** 2.93 mas. This translates to a distance of about **340 parsecs (~1100 light-years)**. The object is relatively close to us, *in front of* the main mass of interstellar dust in the Milky Way.
- **Color index (BP-RP):** **-0.18**!!!

In astrophysics, the color index BP-RP shows the difference between brightness in the blue (BP) and red (RP) filters of Gaia.

- For the Sun (a yellow star), it is about +0.8.
- For red stars, it is positive and large (+1.5 and higher).
- **A negative value (-0.18)** means that the star is brighter in the blue filter than in the red. This is a direct mathematical marker of a surface temperature above 10,000–15,000 Kelvin.

**Conclusion. — all independent sources say the same thing:**

1. **The linear FITS** shows the dominance of the blue channel over red and green (after Bayer correction).
2. **The Gaia DR3 catalog** shows a negative color index (BP-RP = -0.18).
3. **The distance (~1100 light-years)** confirms that this is a local object whose light has not had time to redden due to galactic dust (which rules out distant quasars).
4. **The absence in SIMBAD** is explained by its faintness (19m), which is typical for white dwarfs discovered only thanks to the ultra-precise Gaia telescope.

**This is a white dwarf that has not yet been entered into catalogs, as I understand it. Searching by coordinates in SIMBAD gives nothing.**